. This is a full stop. It tells people you've just made a point, generally it seperates one idea from the next in things called sentences.
, This is a comma. It helps the sentences flow by adding little pauses, like breaths.

Finally, it's all about location!
Choosing the right forum for help can be very useful, for example you wouldn't ask a boat question on a car enthusiast site. Why, people might think you're a fkn moron for posting something so vague.

Thanks, and have fun! :D