In order to help you start out here, the following are the three main sections in PF. You should explore them well:
1. The main forums, that you see in the first page.
2. Insights Blog, available at the top row (header section). In short, they have been described as a "wonder of the web". It contains articles that help in learning topics to a great extent.
3. The Videos, also available in the header section. The media gallery now has some great videos in almost every aspect in science, and they provide an audio-visual learning experience.