Click on the box opposite the layer in the left panel to make the layer visible / invisible.
With buttons 1 and 2 you can switch the view of the board TOP view and BOTTOM view, respectively. In this case, the visibility of the opposite layer is automatically turned off.
With buttons 3 and 4 you can change the priority display layer of the TOP COPPER layer and BOTTOM COPPER layer, respectively. If you press the button again, the corresponding layer of silk-screen printing will go to the background. Sometimes useful.
When you click on a PCB element, then the elements of the active layer have priority. So for example, if you need to select a track in the INNER1 layer, first make INNER1 layer an active layer by pressing button 5
If you don’t like the fact that when pressing buttons 1 or 2 some opposite layers become invisible and you do not need it, but you want to use these buttons when editing printed circuit boards, then make both layers (Top View & Bottom View) invisible, and these the buttons will work similar to the first classic version of FreePcb. The buttons 1 and 2 to switch the TOP COPPER layer and BOTTOM COPPER layer.