To make it, the heart of the plant is cooked and then squeezed in a stone wheel to extract the juice. This juice is then fermented in tanks until it evaporates and then condenses to become tequila. A good tequila is made 100% of blue agave (one of the 135 species of agave in Mexico), so check the label of your bottle to be sure; it has to have a monogram label of the Tequila Regulatory Council which proofs its authenticity.
There are three types of tequila: blanco, añejo and reposado.
Blanco is the clear one, produced after final fermentation, it has a pure flavor. This is the one that should be used to prepare cocktails.
Reposado is tequila aged in oak barrels for at least two months, its color is slightly darker and the taste is a bit smoother. It can be drank pure or in cocktails.
Añejo is an aged tequila which has been in the barrels for at least one year. It has full flavor and a Woody color. Better drank pure and straight (no lemon or salt).