The best way is to simply use it as much as possible and challenge yourself. I've been working as a developer for nearly 20 years and I'm always finding new things that I don't know how to do. Learning to search effectively is probably the best skill any new developer should hone.
If I were you I'd start out with something not too difficult, like a simple text editor application (make your own version of notepad!) That will give you some basic skills like simple UI design (menus, controls anchored to the form etc.), file reading/writing (good exposure to streams unless you use the quick and easy methods). It's just a general basic all-rounder. Then expand on it - make it so the pages open in tabs. That will teach you about collections (the tab pages, in this instance) or MDI child windows.
There are some great resources available online, but I'll always suggest Stack Overflow. If you don't know it then google it. It's part of the "Stack Exchange" collection of Q&A sites and is probably the most reliable place on the web for programming answers.
Basically, don't try and learn it so you can do it. Do it so you can learn it.
I hope this helps - good luck, and most of all, have fun!