Like futures markets, options markets can be traded in both directions (up or down). If a trader thinks that the market will go up, they will buy a Call option, and if they think that the market will go down, they will buy a Put option. There are also options strategies that involve buying both a Call and a Put, and in this case, the trader does not care which direction the market moves.
In terms of valuing option contracts, it is essentially all about determining the probabilities of future price events. The more likely something is to occur, the more expensive an option would be that profits from that event. For instance, a call value goes up as the stock (underlying) goes up. This is the key to understanding the relative value of options.
When buying or selling options, the investor or trader has the right to exercise that option at any point up until the expiration date - so simply buying or selling an option doesn't mean you actually have to exercise it at the buy/sell point. Because of this system, options are considered derivative securities - which means their price is derived from something else (in this case, from the value of assets like the market, securities or other underlying instruments). For this reason, options are often considered less risky than stocks (if used correctly).