What are movements?

So, a lot of songs have different movements, and I don't know what they are! most of the time, movements of the same song have a completley different melodys, and are just in the same music genre, and I use FL studio where you just click to add notes and choose an instrument. can someone tell me what a movement is?

Not to belittle anyone or be pretentious, but I think it's best to use the correct terminology when discussing these things.

A piece can have several movements. Think of the piece (for example, lets say Beethoven's 5th Symphony) as a novel, and a movement as a chapter of that novel (in our example, there are four movements in that symphony). Movements don't have to be similar (melodically or harmonically) and can have varied moods or personalities. Pieces can have anywhere from 2 movements to infinite (a bit impractical and illogical, but theoretically possible). Most of the time, there is a unifying element that tie together the movements, be it musical or external narrative. There are cases where movements are so different from each other that they can be their own pieces, but that is a rare occurrence. 

In classical music, a piece is like an album and movements are like songs in the album. The main difference is that usually people don't listen to movements out of order, since the order is important to the flow of the music, but that's pretty much what a movement is.