Puts are option to sell a stock. Calls are options to buy a stock. The book I
use for my students at Seton Hall is Options As A Strategic Investment by Larry
McMilan.

correction. got ahead of myself. if youre short, you must buy a call for
protection.

thats probably too long to answer on here. going to the CBOE would be good.
there are whole books on how options work. i guess in laymens terms they are
like insurance policys. if im long a stock i can buy a put as insurance against
its decline. if im short, i can buy a put for the same thing. if im selling
options, im simply selling other traders the insurance they are looking for.

You can find all definitions related to the market at investopedia.com.
You can read through the information on http://www.optionmonster.com/ - it's
very informative.
Options, the whole suite of option products, are very complex and involve much
more than a belief a stock will go up or down.