Welcome to the Krita Manual! In this section, we'll try to get you up to speed.
If you are familiar with digital painting, we recommend checking out the introduction coming from other software category, which contains guides that get you up to speed with Krita by comparing its functions to other software.
If you aren't, just start with Installation, which deals with installing Krita, and continue on to Starting Krita, which helps with making a new document and saving it, Basic Concepts, in which we'll try to quickly cover the big categories of Krita's functionality, and finally, Navigation, which helps you find basic usage help, such as panning, zooming and rotating.
When you have mastered those, you can look into the dedicated introduction pages for functionality in the User Manual, read through the over arching concepts behind (digital) painting in the General Concepts section, or just search the Reference Manual for what a specific button does.