Well, hmm first youd have to settle on a style you wished to use. Although in my personal opinion its better to just start with the basics such as getting a body frame down. https://i.pinimg.com/originals/88/72/bc/8872bccb74fd167bbf561686765065d2.jpg
Notice how a bunch of artists simplify the anatomy of a pony to a circle for the head, a bean for the main trunk of the body. A line for the spine. And four lines for the legs. Try doing that a bit until you feel comfortable to begin adding other things like joints,hooves, ears, eyes, snoots.
Drawing them in krita will be no different that drawing them in other art programs, although some programs like PaintTool SAI have antialiasing that helps make lines look way cleaner and smooth.
Make Sure to use a pen/pencil tool in your program that youre comfortable with.
I personally downloaded a brush pack because it had some brushes I felt more comfortable sketching with and I suggest you give it a go too.
If you need help installing them dont hesitate to ask me, its pretty simple too.
If you want to search for more in depth tutorials for pony anatomy I suggest using pinterest as its like a massive collection of ideas and art concepts you have at your disposal for references.
Thats another thing: references. Make sure to always have a picture reference nearby, it'll help you cross reference what youre drawing with what you want to draw. As such you'll be able to compare them and see were you went wrong and were you went right more easily so you can go back and fix mistakes or repeat success. Dont be afraid to get things wrong, be afraid of not trying things. Polishing your craft takes time and all success has like sixteen failures that lie behind it.