Options trading involves buying and selling options contracts. These contracts give you the right, but not the obligation, to buy or sell an underlying asset at a set price on or before a certain date.
A Call Option gives the buyer the right to buy the underlying asset. You typically buy a call option when you expect the price of the underlying asset to go up.
A Put Option gives the buyer the right to sell the underlying asset. You typically buy a put option when you expect the price of the underlying asset to go down.
Differences also exist in terms of risk. When buying options, your risk is limited to the premium paid, but when selling (writing) options, risk can theoretically be infinite in the case of naked calls.