Anyway this is Doodlebuddy, one of my first and favourite drawing apps. This walk thru to drawing a face with it - more of a doodle face than a portrait, but you can do a portrait if you work from a model or photo.
It's so much like working with pastels I want to wash my hands afterwards... My complaints about it are that it's slow at startup but then it's a powerful program, that a phone call interupts it and you lose your unsaved changes, and the limited pallette. But it's free and for that price i like it a lot!
Step 1: Select base color and size of brush
Select your brush by touching the colour then go back into the brush menu to set the size using the slider at the bottom. You can set the size first then the colour in one step but I always forget.
Then make a mark that suggests the outline of the face. If you don't like it, you can use the undo button at the bottom left of the screen, or the eraser in the brush menu, or keep scratching at it with more colour till something pleasing emerges.