Making holes in Fusion 360 is straightforward, so this section will be brief.
Sketch Tool → Select the Base of your CAD model. → Sketch the shape. You can use the circle diameter or 3-point circle tool for the circles.
For any none regular shapes like the ovoid in our original model– Draw intersecting straight lines, trim them down, and then use the filleting tool to sketch the curves.
Once finished, extrude and cut again.
Now, we’ll do the same for the wall’s circles. Sketch the circles, then do an extrude cut.
There we go. All the hole-cutting is done. However, some of these holes still need some work.