In Google Drive create a Google Drawing and add one square to the drawing and put it at the bottom of the screen.
Duplicate this drawing and create an example of a pyramid with 10 squares on the bottom row.
Create an Assignment in Google Classroom and add the Google Drawing so that each student has a copy. Also add the example so that students can see what a finished pyramid might look like.
NB: If students have joined the classroom already, they will not need to do the second task above!