Since it first launched in 2005, YouTube has quickly become the number one destination for video content online, attracting over one billion regular users. YouTube is full of great stuff. It's also full of rubbish! But if you're a visual person and learn by watching, rather than reading, then it's a great place to find information on how to do things, find music, find reviews and it's a treasure trove if you persevere with it.
If you prefer to read how 'stuff' works this wikipedia page will tell you all about Bookmarks; what they are, how they work and why they are incredibly useful.
IMPORTANT NOTE: It doesn't matter what type of computer, tablet, smartphone you use. YouTube works in the similar way across ALL operating systems.
This review of YouTube gives some idea of the power and the frustrations of using Moving media.