If you just google testosterone or free testosterone, you're going to get a lot of random stuff. Google ranks pages very specifically, so being specific with your search terms will get you more.
Search around on Pubmed and other medical literature sites for what you think it could be. These operate similar to google in that you'll need to be reasonably specific.
Some search terms you'll want to use for your situation:
Normal testosterone in adult males
Normal free testosterone in adult males
Symptoms of low testosterone
Relationship between cortisol and testosterone
Testosterone and depression
testosterone and libido
a little tweak to your keyword search can have a big impact on what results you get in the search engines. Broad search = broad results. If you refine things or even make it an exact match using quotation marks i.e, "testosterone and depression", you'll get whatever the search engine can find with that exact phrase.