First thing you have to do is quit thinking about the on chip ram as some sort of special place to put data. Every variable you make is stored in on chip ram, every array, every byte, every x var byte : x = 10 x is ram, ram is x.
If you have an 18F2620 and you:
temp var byte[1023]
You have just allocated 1024 bytes of on chip to be declared as an array by the name of temp to be accessed with a statement such as temp[586] = 56.
Ah things are becoming less foggy now. As you might have guessed I'm new to programming in general. Thanks for being patient