To launch editor wtite "BrushEditor()" in the console.
Currently avilable tools: Square, Filled square, point.
To use Square or Filled square press to select first point and press again to selcet second point.
RMB - Erase
LMB - Draw
You can find saved brushes in the folder "Brushes" in the tpt directory.
After saving restart tpt and you can now select your brush using Tab key.
Demo:
How do I delete a brush that I made? I can't find the tpt directory
instructions for removing brushes(titanic thanks to LBPHacker):
1) click on settings (checkmark in the corner of the screen)
2) scroll down and click "open data folder"
3) open the “brushes” folder in the window that opens
4) delete the ones you want