Is this the same as setting RA0-7 to either a 1 or a 0? 1 meaning the RA is analog and 0 meaning it is digital?
I'm not sure that a very helpful way to view the situation. Generally PIC devices have 1 single ADC who's input is connected to a multiplexor, in turn the inputs to multiplexor are connected to external pins.

I don't know what device you are using so I can't go into specifics but for example on a 18F4550, ADCON bit 5-2 determine which multiplexor input is connected to the ADC. Bit 1 is set low to initiate a conversion and will go high when data is available. Bit 0 enables the ADC.

ADCON1 bit 6-7 allow you to offset the top and/or bottom reading of the ADC. Bits 3-0 determine which possible multiplexor inputs are used (analogue to use, digital for GPIO).

ADCON2 bit 7 determines the formatting of the 10 bit result in the high and low result registers, bit 5-3 set conversion time and bit 2-0 determine the ADC clock source.

If you take your time, set each bit in turn. It's helpful to use binary notation as it show exactly what is set and what is clear.

I hope that helps.