1. Tap on the icon that looks like a pen nib on the left toolbar.
2. Tap three points on the screen, more or less where you would like the three corners of your triangle to be. Don't worry if you are inaccurate at this stage.
3. Tap back on the original point to close the triangle. This has made a shape which can be moved, coloured in, rotated etc.
4. To change the triangle in any way, just move any of its corners.
5. Use the red dot to rotate it.
6. To align it at a specific angle, tap on the adjustment menu icon (four arrows pointing north, south, east west). In that menu, there is an angle option. Just tap on it and write in the angle you want.
7. Two more ways of making triangles are (i) dropping a three sided polygon (pentagon icon on the left toolbar) into a drawing and then moving the corners to make the triangle you want; and (ii) going to the shapes library (drawers icon on the left toolbar, select shapes), dropping a right triangle into your drawing and moving the corners to make whatever triangle you want.
As always, I would love to see what you make with Touchdraw in my Flickr group.