Hey,
When I am installing a MCR in my logic and I need to use an internal coil, where does the addressing start for internal coils? ie: 0:8/0...etc.?

O is for Output. File B is use for relay logic instructions. example B3:0/0.
Is bit. if you want to tell internal relay, ok. but still bit remains

Couple of points here, Told is correct for SLC500 PLCs and earlier using RSLogix 500 or RSLogix 5. These PLCs are absolute addressed, as older PLCs tended to be, and the default Boolean file was B3, thus addresses started at B3:0/0. But you could create further Boolean files starting after the last used default file, which as I remember is file 9. So addresses from B10:0/0 upwards are also possible. A well written program would make use of these possibilities to create some logical structure in the register allocation.

In any case, the key point is that Logix series controllers (Rockwell tell you off for calling them PLCs) work completely differently. There is no absolute address. You create a Boolean address as you need it and give it some kind of appropriate name. There is no associated absolute address. Now that does not begin to cover how best to allocate registers in RSLogix5000 programs. Again that is a huge subject. Suffice to say that the possibilities are far greater than they were in RSLogix 500 and earlier. One thing you might like to look into as a first insight into that is to understand the difference between using an alias in an RSLogix5000 program and mapping one register to another in more traditional PLC programming languages like RSLogix500.