First thing you will notice is that it is split into two - Bank 0 and Bank 1.
Bank 1 is used to control the actual operation of the PIC, for example to tell the PIC which bits of Port A are input and which are output.
Bank 0 is used to manipulate the data. An example is as follows: Let us say we want to make one bit on Port A high.
First we need to go to Bank 1 to set the particular bit, or pin, on Port A as an output.
We then come back to Bank 0 and send a logic 1 (bit 1) to that pin.