I would like to take a moment and address a few things that will make it easier for me to describe things to you later. In a micro we refer to a binary number like 1111 as 1111b, a decimal number like 123 as 123, and a hex number like A5 as A5h. So don't be confused by the letters following numbers, it is easier than having to say the whole words binary, decimal, or hexadecimal, but still indicate it. By doing this, there is no doubt what base a multidigit, or multibit, number is in. Also there is another kind of memory, called flags.
Flags are single bit numbers used to indicate different conditions.
They are called flags because they flag the program of events or conditions. One other thing, in an 8 bit byte the 8 bits are referred to as bits 0 through 7, with bit 0 being the right most, or least significant, and bit 7 as the left most or most significant. Lastly, there are various Registers inside a micro. These vary from micro to micro, but all contain a register called the Accumulator. It is also referred to in some as the a register.