Now, before you get too excited, there's not really much you can customize by default. What you can do is change the gestures for "Swipe between apps," "Swipe between full-screen applications," Mission Control, and Exposé. If you don't like the gestures that are assigned to them, you can change them in System Settings > Trackpad > More Gestures.

If you do want to really create some custom gestures, you can opt to use a tool like BetterTouchTool, which is the best option for creating custom gestures. With this tool ($15 one-time for a standard license), you can create gestures for almost anything. For instance, I create a one-finger circular gesture to open the app switcher.

If you're serious about creating custom gestures, just buy this app and start customizing.

Hot corners are simple: you assign something (like showing the app launcher or the notification panel) to a corner, and when you move your cursor to that corner, whatever you've assigned to it happens. My hot corners are: top left -- Application Windows, bottom left -- Mission Control, top right -- Apps, bottom right -- Notification Center.