It is not ready yet. We will make series of tutorial soon

Yes. But currently i dont have plans to add that, sorry.

Few users requested that, i will do it.

Both there request will be added soon - probably in version 1.1.

If you want to create brush with your own "stamp", "aux stamp" or "pattern" - first you have to preapre the image.
Stamp Image can be any size and ratio (square or any rectange). It must contains black (or gray) shape on white background, for example black circle on white background.
After you create the image, tap File->Add Preset->Add Brush Stamp Preset. Make the same steps to create Aux stamp.
Pattern is similar - create image, brushes uses only grayscale patterns, so it should be grayscale.
After you finish tap File->Add Preset->Add Grayscale Pattern Preset.

Now you can start working on the brush. Choose any tool that needs brush, for example Paint tool.
Choose any brush that is similar to the one you want ot create. To set your own stamp go to Stamp, choose Generator-Image, tap on Image below to open Stamps library. Your stamp should be there. The same steps to set aux stamp and pattern

After you finish working on the brush you should save it - drag brush preview (zigzak at the top) to the list at the bottom of Brush Editor popover. You can also tap "Gear" icon at the bottom-right, and choose "Add Current".

Liquify - we will add this probably in version 1.2 at the beginning of the next year
Warp - it is also on our ToDo list, later next uear

You can add reference photo as a separate layer. Then use Edit->Transform to scale/move/rotate it.
To add photo as layer tap Layer->Add->Add Layer From Photos