A reply to /u/themantheycallsven
You may want to read /u/mi13 's answer here
Well, it depends on what you mean by "medieval times." In the early middle ages, then yeah, most armies were primarily made up of militias. For instance, in Anglo-Saxon England (I've got a friend who does Anglo-Saxon history, so I've heard a lot about this!), the bulk of the military was made up of the fyrd who were for the most part, conscripted peasantry. The experienced nucleus of the army were the comitatus who were the professional retainers/bodyguards/goons of the noble class. (See also: thegns or housecarls) but they were relatively few in number compared to the militia. For example, at Hastings, Harold's housecarls fought to the death, even after their king died.
Basically, you only start to see professional armies in the later middle ages because earlier governments were too decentralized to support them, and a centrally organized army was something that local nobility had no interest in seeing (After all, it could be used against them!)
Now, whether the peasantry had no experience is hard to say, but it'd be likely that some would, just because they survived past campaigning seasons.
"Medieval Times" is an extremely broad descriptor that covers hundreds of states over hundreds of years. Sometimes some nations would maintain a professional army, sometimes they would hire professional mercenary bands, but a lot of the time the state didn't have the money or organization and they would rely on less-trained militias. The exact ratios varied depending on what country you're talking about, and when.
But to say they had no prior fighting experience and improvised weapons might be going a little far. While spur-of-the-moment conscription of farmers happened from time to time, that was more of an extreme emergency measure. Most militias would require members to meet and train now and then, so they would have some experience, and some equipment- either provided themselves, or kept by their lord at a central armory to be distributed on outbreak of war.
When weapons were improvised, (when a militiaman was expected to provide his own spear, or when a general populace was mobilized for an emergency defense, or when an army wound up with more men than it had weapons) they usually had better options than simple sharpened sticks. In Europe, at least. Bamboo spears in the east were a little more practical.
Many polearms' designs come from re-purposed farm implements. They might not use a pitchfork straight up, but quickly reforge the head into a simple spear. Scythes would be remounted to be perpendicular to the shaft to make simple polearms. It's one reason (among others) that spears were a popular weapon for the bulk of an army- since many peaceful tools used a similar design, it was very easy to supply a lot of them.