When should place comma before the and in an English sentence?
I use Grammarly for checking my grammar, and it suggests me to add a comma each time I use and.
For example, "What you need to do is to create your website, somehow attract visitors, and place Google ads on your web pages."
Or such example: "I like blueberry, cherry, and grape."
I thought, should add a comma in front of "and" only when it connects two sentences.
I thought I should not add a comma when I list the items like in the second example, but Grammarly forces me to insert a comma. Is it correct for US English?