Blender how to cut a hole in your object

Here is a tutorial I study from the youtube

The summary
1. Press "tab" to go into edit mode, press "A" to select all
2. On left panel, choose "subdivide" , cut it 4 or 6
3. Choose the middle part, press x to delete its vertical, now you have a hole in your cube
4. To make a circle hole, you need to first select the edge of your hole, click "MESH" on bottom then MESH -> SNAP -> CURSOR TO SELECTED
5. Press OPTION+SHIFT+S (on IMAC) then you got your circle hole