Here is a diagram (excuse its roughness)
I should have given Jack and Paul's father a name - lets call him Edward
Cousins have to be of the same generation i.e. first cousins have to share a grandparent with each other (in the case Edward), 2nd cousins have to share a great-grandparent (Edward), 3rd cousins have to share a great great grandparent etc etc
Now looking at the diagram we see that Robert and Michael are 1st cousins.
Now we look at Robert and Peter. They are 1st cousins once removed.
Robert and Stephen are ist cousins, twice removed.
Robert and Tom are 1st cousins, three times removed.
Now look at Peter and William, they are 2nd cousins.
William and Stephen are 2nd cousins once removed,
William and Tom are second cousins, twice removed.
I hope that that all makes sense.