What does it mean when people write "ha" at the end of their sentence?

[JessiJames2001]

When I chat with people on facebook etc, they often write a sentence, and then they end it, or start it with a "ha". For example today I was helping my friend out with an apartment and this is what he wrote me back: I sure will!! "Jewels, words cant describe how cool you are! ha" Often they can start with it too "Ha, I will try that"...
What does it really mean?