Could someone please clarify somthing that has been confusing me for a while?

From what I understand, people who do a four year course in Poland (usually North Americans) often spend the final two years of their course back in the States doing "clinicals". Can someone explain exactly what these are and more importantly, is the end of the second year, therefore, the end of their contact with whichever university they were studying at? Do they have to go back to Poland for further instruction or do they gain the rest of their training "on the job" as it were? If the latter is true, why do they still have to pay tuition to the university?

Maybe I have got this totally wrong but I would be grateful if someone could clarify the situation as it is an entirely foreign system that I am considering venturing into.

I've tried searching threads to find an answer but have come up with little so far.

Many thanks.