Hi Anze,
Yeah, you can go in Edit Mode for the cube, go into vertex selection, pick the corner vertice, go to the Mesh drop down menu, go to Snap and pick Cursor to Selected (you can also use the pie menu Shift S to get the snap menu). That will put your cursor on that vertice and then you can snap the sphere with the Selection to Cursor in either Object Mode or Edit Mode.
Also in Object Mode, you can also turn on and use the Vertex Snaping setting and snap the sphere right onto the corner of the cube while moving the sphere
There a several basic courses that will better guide you in all these areas. Keep going and it will make sense and make thigs clearer more and more as you keep experimenting and trying. And of course ask questions there are great instructors here that give great help and advice.
I hope this helps
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