First, 'Banksel', this is a macro that produces the required code to switch to the correct 'bank', this is where the GPR's (RAM) and special registers are held. This is 'bank selection', and is set by bits RP0 and RP1 in the STATUS register.
The second point is switching 'pages', this is program memory (essentially ROM), and it's arranged in 2Kb pages - the bits in PCLATH select which page you are using. This is 'page selection' and is set by bits in PCLATH, which are effectively the upper bits of the program counter PCL.
The two 'BCF PCLATH' lines clear the PCLATH bits, and mean the first page is selected. If you use a 16F628 it only has 2Kb of program memory, so paging doesn't apply!.