#1
I see the letter above the lyrics, but do I need to know the strumming pattern in advance, or just strum on the lyrics? Sorry, still new to all this.
#2
If I understand what you mean, the letter (chord) on top of the word usually denotes when you'd change to that chord.

So when you're listening to the song and the singer says the word, you'd hear the guitar switch to that chord.
The content of this signature is pretty much irrelevant
#3
What the user above said and for the strumming pattern, unless it is noted in the tab beforehand, just strum what sounds right. There is really no 'correct' way to strum a song.
GEAR:
Epiphone Les Paul Studio Deluxe
ESP LTD EX-360
Peavey VYPYR 30W

"There's nothing constant in the universe.
All ebb and flow, and every shape that's born,
bears in it's womb, the seeds of change".