Article: Bendy straw work the best, but you can try it with a normal straw as well. It just needs to be long enough to reach from your armpit to your mouth. Take one end of the straw and close your armpit around it. You can do this with a shirt on if you stick it in through the collar. Put the other end of the straw in your mouth and blow. It should produce realistic sounding fart noises with ease.

What is a summary?
Find a straw. Put the straw in your armpit. Blow to make fart noises.