I'm a beginner. I have been practicing this song but I have a question about the part that repeats "I know, I know". The tab says to strum the A during this part. But what does that mean? Do you just hit it on the way down and keep the rythym or on the way up as well?
I could j/k that strumming the A is some kind of sex thing. And that yes, if that's your sort of sauce, then hit it. Hit it good. With good rhythm. Up and down. Up and down.

But seriously, please read the FAQ. This is the wrong forum. You want guitar basics.

And play the A with rhythm, but alternate pick or not, it's up to you. Maybe use the chord A, as this will result in a fuller sound.

Reported, for closure.

A thankyou.