Installing Mods on Mac

I want to be able to play a modded version (really any of the mods), and I followed this video X and did everything exactly as he said, and it didn't work. My guess is that something changed in 1.3.1, because the video is still in 1.3.0.8, and tModLoader is still 0.7.1.1.

I've tried using that version of tMod, and the newest, but I can't seem to get any results. Anyone have any suggestions?