Building lipos?

Ok, Im sure this has been asked a few times, but I couldnt find it

My buddy has 2 flight power EVO lite packs that each have 5 or so run on them in his heli, there 18C, 1320 mah packs

He said he will give them to me if I want them, and I was pondering about taking them apart, and making a 3s pack, so with that said

How hard is this to do? Is it just positive to neg? Do I need to put something inbetween the cells so they dont short?

I probably wont do the balancing leads just because I will be buying other packs, this is more a pack to get me going

Thanks!