PineappleDood

Ive been wanting to put on a straight pipe on to my 06 silverado fora while now but the weather has just now been starting to get warm. I found a video that i think is the most complete instructional video for putting on a straight pipe but its not for my truck and i dont want to assume anything and damage it. i was wondering is there anyone willing to give me step by step instructions to putting a straight pipe on an 06 silverado? i am going to leave the catalytic converter on.
also when i go to the store to buy a pipe, what do i measure to give them the right dimensions? diameter or circumfrence?

thanks in advance!