Earlier quoted context omitted.
On a more general note, anyone know of any good guides/articles describing these sorts of bets? I often have a sense of where a stock price will go but have no idea how to take advantage.
Just note, the poster most probably did not actually 'short' facebook, the poster used options to do this. Its pretty simple for the buy case. Options have a strike price and an expiration date. You buy a CALL option, with a strike price, that gives you an option to buy that stock for that price. Or you can buy a PUT option, that gives you the option to sell at that strike price. Example using made up numbers. FB is…
I think you mean theta decay. Theta is the time factor of an option's value.
Beta is, roughly, a comparison of a security's (or portfolio's) volatility versus market vol.
https://www.investopedia.com/terms/b/beta.asp
Beta decay is studied in a completely different industry.