Looking good, a nice start!
Great advice from the guys above. It is great that you are setting out how to learn how to edit your own images.
I don't know how you would do it in other applications but if they are similiar to Photoshop, the way I would cut out the window in the layer that goes above the other days is:
- create the cover layer as mentioned above and adding what ever detail you want on it
- with the "magic wand" selection tool ( or similar ) select all of the pixels that make up the date window. You should end up with a selection that is the same shape as the window but it will look a little larger due the feathering of the edge ( it fades gradually to invisibility ).
- now, keeping the selection, change to your new cover layer, re-feather the selection to make sure that the edges are smooth, and delete/cut the selection from your layer.
Now that you have your cover layer, the order of layes would be is:
bottom: background layer ( needed because it may be possible to see throught the edges of the overlapping feathered edges between the day window and your new layer ). You can just rely on the background colour for this if you want but only if the colour matches your face. Otherwise, you will need to put a new layer here ( you could simply duplicate the top layer and use that ).
2nd layer: day window
3rd layer: day circle
top layer: your new layer
If the cut-out in your layer turns out to be too small/large then just repeat as above but expand/shrink the final selection before you cut out the window in your layer.
I hope that helps.