The last chord in the song is the key tone 90% of the time. The only time it isn't is if it's jazz, where they tend to end on a chord other than the tonic. Or some weird "incomplete' effect. Most music will end by returning to the tonic chord because it sounds like home, giving the movement a sense of completeness.

Watch the first chord in the chorus, alot of times this is true but there are songs that will change keys for the chorus. Usually relative keys, so if the verse is in A minor the chorus might be in C major.

Doesn't seem like an issue but it's a good idea to keep the tonic note in mind while jamming because it's a goal in music to get there at some point. Ending a A minor sequence on C will sound off.

Listening and feeling is the most important thing in music.