For simple, single-line comments, use the semicolon ; followed by your comment.
add a,a ; Multiply a by two.
For longer comments, you might find it easier to switch the assembler off using the .endasm directive.
.endasm This function calculates the product of H and L. In: H = Operand 1. L = Operand 2. Out: HL = Operand 1 × Operand 2 .asm HtimesL: ; ... ret