Calls vs Puts
Every option you will ever see — every spread, condor, and butterfly — is built from just two pieces: calls and puts. Get these two right and the rest is only combination.
A call is the right to buy. A put is the right to sell.
A call gives its owner the right to buy 100 shares of a stock at a fixed price (the strike) up to a fixed date (expiration). A put gives the right to sell 100 shares at the strike. For every owner of a contract there is a seller on the other side who takes the opposite obligation — and collects a premium for accepting it.
That is the entire game: the buyer holds a right, the seller holds an obligation, and premium changes hands for it. Because you can be on either side of either contract, there are exactly four basic positions. Learn to read these cold and most of the library falls into place.