1. Open the Layers panel (Window > Layers)
2. From the panel menu, choose New Layer. In the dialog, you can name the layer if you like Page Numbers.
3. On your master page(s) select the text frame with the page numbers with the Selection tool (black arrow tool).
4. If you look at the Layers panel now, you'll see a small square to the right of one of your layers (or Layer 1 if you haven't created any new layers). Drag the square to the Page Numbers layer. [Explanation: The square is a "proxy" for the selected objects. Dragging it to the other layer moves the object(s) to that layer.]
Create new layer
Switch to Master page
Make sure new layer is on top in the Layers panel, if not drag the layer on top in the Layers panel.
Select (click once on) that top layer (pen symbol appears behind that layer in the Layer panel)
Now draw your page numbers etc on the Mastet page
From now on, select (click once on) any Layer in the Layers panel that is below the layer you used on your Master page items and create new objects in your document pages.
If you accidently created objects on a 'wrong' layer:
Select those objects
You will see a square behind the layers name in the Layers panel
Click and hold the mouse on that square and drag it behind the name of the layer you want to move the objects to.
Buy a book about InDesign and start learning these basic principles!
Thank you so much! Your instructions were so clear!