Hey I'm looking to order a fuse holder off a site...I'm not sure what fuse size, if its talking about my amp or the truck its self.

take a look.
http://www.tti-plus.com/Bluewave-Pla.../bw-anhs21.htm

it says "please select fuse size." I Don't know what to put.

Couple days old but

What size and brand of wire are you running?

well, i run a 400wrms mono amp and a 75x2wrms 2 channel off a 60amp. Depends on the fuse type, I'd start with a 60amp and if it blows go to radio shack and up it 1 size. There is absolutely no reason to have a fuse larger then the main car fuse.