Excel macro to check for certain rules and insert comments on a cell

I am trying to create a macro that will automatically review an excel sheet for certain rules:
1. The excel sheet has software test cases
2. If a cell (in column D) has a text value of 'Yes' then the corresponding cell (in column B) should have the word 'Screenshot' if not then a comment should be inserted on cell in column B, like "Error".
Kindly help.