How do you evolve Pokemon in Pokemon GO?

Evolution in Pokemon GO is dependent on candy. You slowly collect candy of different types as you catch Pokemon of that type (if Pokemon are evolutions of each other, the candy will be named after the lowest evolution).

On the screen for an individual Pokemon, it will show the cost of Powering Up or Evolving (if it doesn't show the price of evolving, then evolving is not possible... that Pokemon may not have a higher evolution).

Usually the cost will be 12 candy for common or lower level Pokemon, and 50 for others. You get 3 candy for catching, and 1 candy for transferring a Pokemon of that type to the Professor.