In the first example the operand is the constant 0. This operand provides a value for the assembler to place in the storage created and named SumOfDivs. Since addition is a binary operation the addw instruction requires two operands. Instructions generally have two, one or zero operands. There are a few special instructions that have three operands.
Assembler directives can have many operands, often in the form of a comma delimited list.
They are often placed at the end of a line and consist of a brief description of one or a few lines of code. It is possible to have a line that is all comment. In this case the first thing on the line should be the semi-colon, for example. The processing of comments has one quirk in the Next's c compiler that you should be forewarned about. For some reason when the compiler is processing a comment it is still views apostrophes or double quotes as initiating a string and insists on the string being closed.