A few weeks ago I went back to the gym after a short hiatus of *ahem* five years or so.  So I needed gym shorts.  I bought three pairs, and they all came with one of those continuous loop drawstrings.

I'm not a fan of these, but since I'm not planning on returning my dirty gym shorts any time soon, here's a video on how to tie a single loop drawstring.

This certainly isn't the only way... I just couldn't figure out the other diagrams and videos I'd seen, and my way works good enough for me (quick & easy).