>>1020814 (OP)
Go to Mesh Data Properties (the tab with the upside down green triangle, to the bottom right) > Normals > Auto Smooth > 30°
You can also go in Edit Mode > Select Edges > Press your right mouse button > Mark As Sharp, and in the Mesh Data Properties set the degrees to 180°: this will essentially allow you to manually define which edges should be sharp and which not
>best way to make a hole or hole shaped stuff, wich is usefull for modeling guns and vehicles
It's "useful", with only one "l".
You're very rarely going to need a circular hole in a square shape, the only example I can think of is a muzzle break for guns. I advise to rely on Cylinder and Cube primitive shapes instead, if you need to make a barrel of a gun, add a Cylinder to your scene > Inset top and bottom faces > Select the edge loops around the holes > Bridge Edge Loop