When you start out you have access to Forest Haven and Dark Forest. Forest Haven will let you level up to level 13, and Dark Forest will allow you to level up to level 18.

At this point, you must purchase additional dungeons/maps (Balefort Castle is the next map, allowing you to level from 18 to level 23) with "Platinum" which can be acquired through purchasing with real world money through the platinum store (you can also just go to the map and click on the area you wish to buy and click "purchase" at bottom, this will direct you to the platinum store). You can then decide which Platinum coin package to buy, the bigger the coin package you buy the more coins you get for your money, each package becomes a slightly better deal then the last, so you will have to find an amount that you are comfortable with.

You do not have to use a credit card to buy platinum, in fact you can do it by simply going to your local grocery store and buying a iTunes gift card. Then redeem it into your iTunes account. Jump on Pocket Legends and click "purchase" on the coin package you wish to buy and it will take the money directly out of your iTunes account. Fast and simple