When you're writing a list, use commas between each item in your list. Use and between the last two items, instead of a comma. For example: Today I need to buy milk, bread, apples and potatoes.

All this may seem abstract and difficult to put in use. But in fact, there’s a litmus test — two, really — that can help you get these right with no brain strain at all. The name ...

We use a comma to separate dependent and independent clauses, but only when the dependent clause is first in the sentence. This sounds complicated, but it’s not really.