This is a Mac Pro:
This is a PowerMac G5:
Note the difference in the front in terms of the number of optical drive bays.
Note they are both tower desktop machines.
For PowerMac post here:
For Mac Pro, post here:
For MacBook Pro, post here:
The Mac Pro is a desktop with an Intel CPU.
The MacBook Pro is labelled MacBook Pro on the screen frame.
If you see no text below the screen, it is attached to a computer typically under the desk or on it.