How Does Summoning Work?

[inkpenavenger]

It's going to be a while before I get a chance to look at PHB2, so could someone explain the new summoning powers to me in a nutshell? (I'm planning to use the same mechanic in some GSL products I'm working on)

Does it work like the powers that Clerics have that conjure astral guardians and such? Just that with the Summoning keyword?

I appreciate it!