Very straight forward:

1. Add a new transparent layer
2. Use the rectangular selection to define an area
3. Fill with colour and repeat for second block

4. Using the move tool, select the picture layer and shift it down.
Recommendation, click in the canvas to set the move tool but use the keyboard down arrow to move (slowly) down. Otherwise maybe set some edge guides and click-drag. Always a chance using click-drag to move off to the side.
5. You can leave the 'outside of canvas' it does not do any harm but if you want to remove it go
Layer -> Layer to image size.

6. Add your text at the top of the stack