When you're starting out on a topic that's new to you, it's often helpful to get a quick overview of that topic before jumping into the details. That gives you some context to help you understand what you're reading. Typically, you won't cite these sources in a bibliography, they're for you to build your own knowledge base. However, these sources will often point you to websites, articles, books, or other resources that you might end up citing.
Some of the best places for these overviews are encyclopedias or other reference sources, yes, including Wikipedia. These overviews should be relatively short and easy to read and follow, and it's always a good idea to look at a couple of different sources from different places to get the best picture.