If you want to stack items behind or in front of each other - say you want to position some text so that it overlays a photo - then use the z-order (stack order) controls on the Properties Panel.
Just tap the item you want to move to select it, and then tap one of the stack buttons to shift the item's position.
Or use the corresponding key short-cuts for these controls (in order of the icons):
- Ctrl + F or Ctrl + Shift + ] Bring to Front
- Ctrl + Shift + F or Ctrl + ] Move Forward one
- Ctrl + Shift + B or Ctrl + [ Move Back one
- Ctrl + B or Ctrl + Shift + [ Put to Back