Great question Tom. Sources can be very complicated but they can also be very simple. The easiest way to add sources is to just hit the source button at the end of the sentence that you want to source.
When you're in a profile in edit mode, look at the bar just above the text area. The last button on the right is a "C"
Click this button and the reference tags are added. Then just type your source into the highlighted area.
To keep it simple, just put what the source is and the link where you found it:
1920 US Census, Dallas, TX, http://www.ancestry.com.restoftheurl/
Will of John Brown found at Ohio State Documents www.ohio.us.gov/secretary/will/john_brown
Just stick with basic sources for now and you'll learn the rest later.
For sites like Find a Grave and Family Search they have a pre-formatted source; just copy and paste this after hitting the C button.
Hope this helps and good luck!