Well, a cam is a conditonal access module. A cam (complete with card if necessary) will open channels with the associated method of encryption.
A softcam on the other hand is software based as opposed to hardware.
A softcam will open certain channels, for instance the current one for your stb will open nagra 2 encrypted channels.
If it is an AU softcam (auto updating) then you rarely need to change it.
Other patches (like tps) require the latest keys to be updated every couple of days.