Until game developers introduce trading, the only other way to collect Pokémon besides catching and evolving them is by hatching Pokémon eggs. You collect Pokémon eggs as rewards for leveling up, and randomly at Pokéstops. Eggs do require a couple things in order to hatch, however.

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First, you’ll need an incubator. Trainers will be rewarded with an incubator with unlimited uses early on for leveling up, and you can collect limited-use incubators at Pokéstops. These are usually good for about three uses. Once you’ve got your egg in an incubator, you’ll need to walk. Each egg will have its own distance requirement, ranging from 2km, 5km, and 10km. Once you’ve walked the required distance, the egg will hatch. The longer the distance requirement, the more likely it will be a rarer or stronger Pokémon. However, don’t neglect hatching smaller eggs. They still yield more experience and candies than if you were to catch the Pokémon.