A comma (,) can be used to separate things in a list.
I like to eat apples, grapes, pears and oranges.
A comma can also be used to show a break in a sentence. It can separate different parts of a sentence and show you where you should pause when reading.
I like swimming, but I love cycling!
With a shake, the dog dried itself off.
Anyway, I like chocolate too.
A comma can make the meaning of a sentence clear and change what you are trying to say.
Let’s eat Grandma.
Let’s eat, Grandma.