This is a really broad question because whilst there's trenches the whole way through the war there's a huge amount of variation in how those trenches were made, who built them, what their purpose what, was the terrain was like etc. Some examples: Trenches in 1914 and early 1915 were often pretty shabby. They tended to be shallower, not well revetted, not well drained with few traverses and fewer armoured posts and dugouts. They could be very muddy and incredibly uncomfortable to be in for any length of time. Because many were so shallow soldiers had to move around hunched over and when it rained they could live in a soup of dirty water, contaminated by the dead and their own excrement.

However, that's a worst case scenario and not all, or even most of the trenches were like that as it depended so much on other factors.

Some generalities though, German trenches tended to be better constructed than those of the British and French. They were usually deeper, about 6 feet, there was much more work put into revetting, which is putting a covering of some kind over the raw earth walls, meaning they held up better. They tended to have proper drainage with raised wooden floors over drainage ditches and sandbag ramparts several feet above the lip of the trench. Along with many deep, concrete reinforced dugouts with multiple entrances, ventilation systems and hardwired electricity this made German trench networks comparatively comfortable, especially along the Hindenburg line.

But fully networked trench systems like that weren't actually a feature of the entire war. By the middle of 1917 trenches were more haphazard affairs again as defence moved away from static lines into defence in depth. This meant fortified pillboxes, block houses and other positions, not directly linked to each other, but mutually supporting. Much more of the thing you see in WW2.

Materially, the lives of soldiers in the trenches was also hugely variable depending on time of year, section of line, where fighting was happening and such like. Conditions for Italian and Austrian soldiers fighting in the mountains of Trentino were very different from those of the British in Flanders which were very different from the French at Verdun.

And in 1918 the return of open warfare didn't do away with trenches, as they were still the best defence against artillery, but as the line changed so frequently trenches were dug more or less for temporary use and lacked the creature comforts that evolved during the more stationary parts of the war.

There were some universal experiences for soldiers in the trenches no matter where they were. One was the strangeness of living life below ground level and having little to no idea of what was happening outside of their trench. They could see the sky and hear the guns, but beyond that they were effectively blind. Vermin were ubiquitous. Flies, rats, fleas and lice were endemic and no one was spared their torment. The smell was atrocious. Burnt cordite, wood smoke, exposed corpses, human waste and stagnant water all mixed together into a nose destroying smell recounted in many memoirs of the war.

If you've got more specific questions I'd be happy to give a more detailed answer.

For the weapons, at least, this old AMA on small arms will likely be of interest.