I have added the line
Uses StrUtils;
at the top of my program, but the compiler or whatever still can't find the file.
Looks strange. It should find it automatically without problems if your FPC installation is fine.
What is the error message?
Where exactly do you put "Uses"? It should go after "program programname;" (not at the top of the program, but after this line). And you shouldn't have two instances of "Uses" (one might be already added automatically). Posting the program code might be a good idea (use # button in edit).
Can you compile the examples? Or anything at all?