Hotkey thread for noobs

I'm struggling with figuring out how to use the hot keys. Can someone explain this to me or point me to a helpful guide? I understand how to make units when I've selected a building, but anything beyond that has escaped me. How do I assign a certain group of villagers or units to some hotkey? How can I assigned certain building (like my town center) to a hotkey so that I can quickly select or go back to that building? What are some of the best practices when it comes to hotkeys? Thanks!