Primary or Secondary?
Primary sources are produced by people "directly involved in the event...either as participants or as witnesses". Sometimes, you will interpret them yourself in your writing.
When to use? When an individual or direct perspective serves your writing purpose
Secondary sources discuss and interpret primary ones.
When to use? When you want an overview or interpretation of a subject
Tips about primary and secondary sources:
The way that you access a source (internet, copy, original, etc.) is irrelevant to determining whether it is primary or secondary.
Some primary sources, like photographs, maps, artwork, and audio and video recordings, are non-written.
Unless you are writing a historiography, you will usually use a blend of primary and secondary sources.
Introductions and headnotes will often provide important information about the author and context of the source.
Both primary and secondary sources need to be evaluated for "reliability and usefulness".
Special considerations for internet sources:
Is the author identified, and if so, what are his or her credentials?
Are there citations and evidence?
Is the site affiliated with an academic institution (.edu sites),.government organization (.gov sites), or other organization (.org sites)?
If it is affiliated with an organization, do they seem biased?
When was the site last updated?
Does the site allow users to change its content?