The ADD instruction documentation from this page has the following table with various encodings:
I believe that imm8 means an immediate value whose size is 8 bits (for example: BYTE 123).
And I believe that r32 means a register whose size is 32 bits (for example: EAX)
But what does r/m8 mean? Does it mean that I can use a register whose size is 8 bits (for example: AL]) or a memory location whose size is 8 bits (for example: BYTE [myvar])?