do i need a capo what dose it do and woud it be usafull i like rock and blues
A capo is in short sweet and dumbed down terms a clamp that in a sense, tighten your string. Using the frets, you can use the capo to change the tuning of your strings by a half step for each fret (makes sense eh?). Careful on using a capo too far down though, if your guitar doesn't have perfect intonation (spelling?) and your capo is misplaced at all you will run into slightly off notes and possibly extra noise (I haven't experienced that but have experienced slightly off notes using a capo too far down the fret board).

They are useful and rather inexpensive though.
a capo is a device that wraps around the guitars neck and holds down all the strings at a certain fret. what this does is essentially change the tuning of the guitar up. most people use them so they can play open chords in different keys. I use mine sometimes to give me a drone note that would otherwise be unaccessible like C.

do you absolutely need one? probably not. but you can get a cheap one for like 5 bucks and they are really handy. they are a staple in most peoples guitar bags even if they don't get a lot of use.
no sir away a papaya war is on
Like this:

There are different types but they all do pretty much the same thing. I use mine almost every time I play, but I do a lot of fingerpicking stuff.
or u can be a cheap ass like i was for a while and make one out of a pen and a shoe lace. probably one of my most ingenious inventions ever. that i spent $20 on a real one and problem solved. not a must have, but it wouldnt hurt to have one. more for acoustic than anything