Kinda, it's more complicated than that. Another player sets down a summon sign and you (while in human form) interact with it when it appears in your world,which will summon the other player as a white phantom. You are allowed two white phantoms at a time and some areas do not allow co op. However while In human form other players can invade you as a red phantom, except rather than helping you they will try to kill you.

I don't even have those spells, nor have I ever been in human form.