How to create a system of random appearance of a model on a selected area?

I need to implement a system for the random appearance of things in a certain area.
I have this place on the map (blue part)

I need to make it so that grass(grass in size is about 1/20 of the full size of the area) could appear on this square in this plane, but I don’t know how to implement it, does anyone have a tutorial for this? (I tried to find it on YouTube, but I couldn’t find what I needed)