when you are looking at a song and you see a chord above a word then the next few words have nothing above them how do you know how many times to play that chord and how do you know if you should strum up or down?
Well, you kinda have to figure out the strum pattern but you strum until you reach the next chord above a lyric, unless you can hear in the track you strum once and then strum agin once you reach the next chord. I hope that makes sense!

As a general rule of thumb you switch to the next chord when you get to the word it's above but you have to listen to the song to know the strumming pattern
Andy Fox
Hard rock guitarist
I play a Jackson DK-2 and an Ibanez RG through a Peavey 6505+ stack