1- Draw a triangle

It will be the inner part of the Penrose Triangle.

2- Extend a line off of each corner.

3- Draw another line off each of thoose extensions that extends a bit over the corners.

'a bit' means 'the same way as in the previous step'.

4- Draw a short angle that lines up with the opposite side.

The size should be the same as in the previous steps.

5- Connect the lines, and you'll get the Penrose Triangle.