Good comments on different sources. You're right that primary sources are those created at the time of the events we're studying. They can also include things like your family's interview with your great grandfather about December 7, 1941, because he lived through the events of that day.

What are the specific things to keep in mind about .com vs. .org, .edu, .gov, etc? Any of them could potentially contain valuable secondary (or even digitized primary) sources. How can we evaluate their relevance and credibility?