To me it looks like your teacher is giving you tutorials that he himself doesn't fully understand. That is unfortunate. That means you must look for answers elsewhere (the reason you came here). Follow @TrippyLighting advise and go through the tutorials offered by autodesk. Also be aware that, like your teacher, folks offering tutorials on youtube frequently don't know what they are doing. It's up to you to figure that out.
In the specific example posted here, it's important to understand WHY the demonstrator is drawing the circle. He's only doing it to create a point to use as a reference for the hole tool. In this specific case it was totally unnecessary to create a sketch with a circle to do that. the existing geometry would have worked just fine.
In our case, begin with the idea that you need a reference POINT to use for the center of the hole. Is drawing a circle the best way to achieve that? No. creating a sketch with either a dimension-ed point or projected geometry is probably what you need to do. Hard to say without your model.
Looking at your object browser, you might consider looking into @TrippyLighting 's rule#1.