The primary sources that will be useful to you depend greatly on the topic you write about. For example, if you are researching a director or actor, you will probably want to watch their movies. If you are researching a comedian, look for their comedy routines.
The places you will go for these sources also differ greatly. For some modern material, YouTube or the internet in general might be the best place to look. Below, I'm going to include a few places you can go within the library and its databases for things you likely can't find through Google.