So I'm building a two-handed weapon character in Pathfinder and was planning on using a longspear, however if I get pinned down, I want a good backup two-handed weapon. Someone suggested a club, as I can swing it as a two-handed weapon. But I can't find any information about using a club like that. Can anyone show me where that's stated?
One-handed weapons can be used two-handed so long as they don't count as "light". When you do, the only change is that you add 1.5x your Strength modifier instead of 1x. A club is a simple one-handed melee weapon (not light), so the suggestion is sound—though I'll refrain from editorialising on whether it's the best choice since charop is not my forte.
Wielding a Weapon Two-Handed
When you deal damage with a weapon that you are wielding two-handed, you add 1-1/2 times your Strength bonus (Strength penalties are not multiplied). You don't get this higher Strength bonus, however, when using a light weapons with two hands.