Progress Bar in WPF

Hello. I have created a little WPF C# app that checks one list of file names against another list of file names. I would like to show a simple progress bar while the lists are being compaired so the user knows the app is still working and did not freeze up. I am having trouble making the progress bar function while the app is compairing the lists. The UI seems to be frozen. I do not need the progress bar to show the exact progress of the function the app is performing; only that is still doing something.

I have read various posts online after a simple Google, but I have not found any good examples of something that works in a straight forward way. Is there an easy way to get the result I am looking for? Thanks.