There are many ways to use a comma. To break a sentance with extra information. For example "Outside my house, which is far from the city, there are a lot of trees." because "which is far from the city" is extra information. A comma is used in a list after each item in the list. For example "I have a house, a car, a bicycle and a computer." however notice that when you write a list the last item does NOT have a comma it has the word "and". For example "1, 2 and 3", "1, 2, 3, 4 and 5". A comma is used for a pause in natural speech, as a way of catching a small breath in the same way that a full stop, or period, is used to pause longer, and take a deep breath.

Try this: http://owl.english.purdue.edu/handouts/grammar/g_comma.html

One thing you could start with is putting a space after the comma before you type something else. I see SO many Chinese and other people do this, probably because when you type you don't use the spacebar as often. For example. When you're here,I'm happy. <---- is WRONG. It needs a space. When you're here, I'm hapy. <---- is RIGHT. :D :D :D So please people, use the spacebar at the appropriate time. thx