Sorry if any of this is unclear/rambly, it's pretty late. I'll put a tldr at the bottom that simplifies it a bit.

Well the Americans were not outplanned. Under the IJN's combat doctrine of Kantai Kessen, the Decisive Battle, Japan's plan was to force the American carrier force into battle by attacking an objective they couldn't afford to lose, Midway Atoll. The Americans, however, had already cracked the Japanese code and were able to determine not only that an attack would take place, but when, from where, and by which ships. So with that knowledge, the Americans set a trap. To say there were outgunned, outmanned, and outnumbered is also debatable, as while the US were only able to sortie with 3 carriers to the Japanese's 4, those carriers not only had larger airgroups (and combined with the aircraft at Midway, the US technically had a quantitative, though not qualitative, advantage in that regard), but were much better protected thanks to both American anti-air fire being superior to that of the Japanese ships', and having more ships escorting the carriers to provide said AA.

Japan went into the battle expecting that the US would only have two carriers available: Enterprise and Hornet. Lexington had been sunk during the preceding Battle of Coral Sea, and Yorktown was so badly damaged that they didn't anticipate she would be repaired and have her airgroups replenished in time. But thanks to the herculean efforts of the repair crews at Pearl Harbor and Vestal, and transferring airgroups from Saratoga to her, she was able to take part in the battle and make it a 4v3. Meanwhile, while the Japanese carrier force, under Chūichi Nagumo, did come into the battle with 4 carriers in Akagi, Kaga, Soryū, and Hiryū, thanks to the inflexibility of their doctrine, neither of the carriers from Coral Sea (Shōkaku, who was badly damaged, and Zuikaku, who was undamaged but suffered severe aircraft losses) were able to participate. Had Zuikaku been reinforced with her sister's airgroups and taken part, things would've almost certainly played out differently.

Getting into the actual battle, the initial Japanese strike on Midway at around 6:20 failed to take it out of action, which would've necessitated a second strike. However, in accordance with the Midway operation, half of the carriers' planes were to be kept in reserve and prepared to launch against the American carriers, should any be spotted. He could wait for the planes that had struck Midway to return, refuel and rearm them, and send them back out, thus saving the reserve aircraft, but that would take a substantial amount of time. But even though Midway was not the primary objective of the battle, the elimination of the American carriers was, for one reason or another Nagumo wanted Midway out of action ASAP, and the reserve aircraft were ordered to be rearmed with bombs for use against ground targets, something which would take a considerable amount of time. While the process was underway, one of the Japanese reconnaissance planes reported the presence of an American naval force, but failed to report its composition. Upon receiving this report, Nagumo cancelled the order to rearm the reserve aircraft and put the original anti-shipping armaments back on, but again, this process would take time. This put Nagumo in a serious conundrum, known today as "Nagumo's dilemma:" Nagumo could either attack immediately with the aircraft he had available, which were only partially armed with anti-shipping weapons and were not in full airgroups (something that went against doctrine), and would run the risk of the returning Midway strike running out of fuel and ditching into the ocean, all for attacking a target which may not even have a carrier; or he could wait for the Midway strike aircraft to land safely and get all the reserve aircraft rearmed, and then launch a full strike on the American force. Being a man of caution, Nagumo went with the second option, which was doctrinal and carried less risk. But around 8:20, the reconnaissance plane sent another report: there was an American carrier present. Nevertheless, Nagumo had made his decision. He would have to wait. The Midway attack group was recovered at 9:10, and now the Japanese carriers should finally be able to launch their strike on the American fleet.

But from 7:55 to 10:00, the aircraft from Midway and later from the American carriers would make a series of attacks on the Japanese carrier force. These attacks would all fail to cause any damage and take heavy losses in most cases, but they played a vital role: they delayed the launch of the Japanese attack. You really couldn't recover nor launch aircraft while under attack, they forced the Japanese combat air patrol to have to land to refuel and rearm and keep the flight decks occupied with them. And so, all the Japanese aircraft were fully fueled and armed within the carriers' hangers, and in the chaotic rearmament process, some of the bombs weren't properly stored.

Also during this time, an American submarine, Nautilus, managed to sneak into the Japanese fleet. She fired torpedoes at a battleship around 8:20 and then a cruiser at 9:10, both times failing to score any hits thanks to the Mark 14 torpedoes being pieces of junk. The destroyer Arashi was dispatched to deal with her.

All these elements set up the fate of the battle.

At 10:00, another torpedo bomber attack was made by aircraft from Yorktown. The Japanese combat air patrol all focused on the low flying torpedo bombers and dived on them, leaving the carrier largely unguarded. At the same time, two groups of American dive bombers were closing in: one from Yorktown coming in from the northeast; and one from Enterprise from the southeast, who were originally off course, but had noticed Arashi rushing back to rejoin the main fleet after failing to sink Nautilus and followed her back home. With the Japanese combat air patrol distracted by Yorktown's torpedo attack and the anti-aircraft gunners insufficient and not expecting the dive bombing attack, the Japanese fleet was caught completely unprepared as the dive bombers made their attacks. Within minutes, every Japanese carrier except Hiryū was hit. The bombs detonated the aircraft, fuel, and ammunition in the carriers' hangars, turning them all into blazing infernos and taking them out of action. Now instead of a 4v3 in favor of Japan, it was a 3v1 in favor of America.

From there, Hiryū launched several counterattacks and managed to badly damage Yorktown twice, but she too would suffer the fate of her fellow Japanese carriers as she was fatally wounded by aircraft from Enterprise and Yorktown later that day. For her part, Yorktown had proven to be damn near impossible to sink, and very well could've been towed out of the battle despite the severe damage she had taken. But unfortunately, she would be torpedoed by the submarine I-168 and finally sunk. The battle was still a decisive victory for the Americans, sinking all 4 Japanese carriers at the cost of just 1 of their own.

---

tldr: The Americans knew the Japanese plan to attack Midway, and set a trap. The failure of the original Midway strike to take the base out of action, poor reconnaissance, Nagumo's cautiousness and adherence to doctrine, and the constant (albeit ineffective) air attacks from Midway and the American carriers constantly delayed an attack on the American carriers by the Japanese fleet and left them vulnerable. And the stars aligned with Yorktown's torpedo bombers drawing away the Japanese CAP, Yorktown's dive bombers attacking from the north, and Enterprise's dive bombers following Arashi back and attacking from the south, all coming together at the perfect time to catch the Japanese fleet unprepared and vulnerable and turn a 4:3 advantage into a 1:3 disadvantage. And from there, devoting Hiryū to a counterattack rather than cutting their losses ensured her demise as well. This video does an excellent job of explaining it all