Well I have a set that was sent to my email . I downloaded it and all the files have .tga behind them .

What does this mean ? Can I use the set or no ?

Yeah you can use that extension. Should work all the same.

Fun Fact: Back in the day all you could use for Toribash was .tga.

Well just something to note .png does work the best .tga and the others work too but .png is still the best

If the TARGAs don't upload for whatever reason (which they probably won't), you will have to convert the format of the files to something more compatible, like .png.

You can use the set if you legally bought it or if it was legally given to you.