Understanding Custom "action." files

Hey,

I'm running a free host, and working on a system that will allow users to buy cPanel hosting for points, the problem i'm having, is the fact that I can't understand your custom "action." scripts, I need a code to be activated when the subscription runs out, that suspends the account, but I could not find any crons ect that do that.

Is there a guide for creating custom action. files?

Thanks,
LibHost

[LibHost]

Bump.