Usually coming sometime after the second chorus, the bridge is a part of the song that sounds completely different than the rest of the song. A Bridge - The bridge is a part that exists in some songs but not all.This is usually where you try to fit the catchiest part of your song (usually called the hook).
What gives away a section of a song as a verse is that the melody is the same but the lyrics are different between the different verses. It is usually fifty percent to twice the number of lines as the chorus but it does not have to be. Many songs do not have an introduction, so don't feel like you have to use it. Sometimes it might sound different from the rest of the song, might be faster or slower, or it might not exist at all. There are standard layouts of these parts that are used in most songs, however, so in order to understand how most songs sound, you'll need to understand the parts. Your song can include all of them or none of them.
