It's cuz I'm dyslexic and I always get things backwards. Which comes first? The file I'm trying to create or the one I'm trying to tar up? Here's the answer for future reference.
tar -cf [the file you want to create] [the file(s)/directory(ies) you want to tar]
The "c" stands for "create". The "f" stands for "file" (the default is to pipe the tarred stuff to stdin). You can also turn it into a gzip file in the same go with the letter "z" or into a b-zip file with the letter "j".