PokeCoinspokecoins are the monetary means for any trainer playing Pokemon GO. PokeCoins allow a player to spend in the Shop in order to buy or upgrade their given items, greatly improving their chances at being successful in one way or another. There are two ways to obtain PokeCoins: by leaving Pokemon at one of your Team's Gyms and claiming the Defender Bonus, or by actually purchasing them with real world money.
Obviously, the quote unquote "hard way" is by earning the pokecoins yourself through the defender Bonus, but if a player wants to speed things up, spending a little cash can easily accomplish that. The defender bonus is great, but since you never know who will try to defeat your gyms, as well as having to hold down a gym for roughly seven hours while your Pokemon are constantly losing Motivation, it might just be best to buy PokeCoins for yourself. That is, of course, if you truly desire to one day complete the game and accomplish the ultimate goals of completing your Pokedex and reaching the Maximum Trainer Level of Level 40.