It depends on what type of music you want to make. In songwriting, there are actually no rules. But if you want to have commercial songs that sell then there are certain conventions that help to follow.
The most popular form is the A B A B C B structure (or subtle variations of it)- A = Refrain, B = Chorus, C = Bridge.
The A part is where we tell the story or build up tension melodically - it leads to the needed release: the B part. That's the catchy thing (hook) that should stick in peoples' heads. The B part should also sum up the song thematically (in text and melody). In the ideal case, the B part is general enough to take on the color of each individual verse so that it gets a new perspective on the same meaning the next time we hear it. It's good to repeat these two parts again so that the ear gets used to the sound and recognizes it as familiar. (It's programmed somewhere down deep inside of people to like what they already know.) But we don't want to bore them to death - So you add the C part to throw in a little bit of newness back into the song. The return to the B part at the end then brings one last warm fuzzy feeling, like coming home. And if your Chorus is as catchy as a hit, people are going to be hungry to hear it one last time.