Here you will find some help, tutorials, and little tips to use Aseprite and start getting the best from it from the very beginning. If you have some question you can start looking at the Frequently Asked Questions.
To get started, you can print the Quick Reference. It contains several keyboard shortcuts, so it could be handy to have it at your side.
Basics: General concepts, elements in the window, expected workflow, etc.
Animation: How to create animations & manipulate frames
Layers: How to handle several layers to compose images
Selecting: How to select
Drawing: How to start drawing