Starting off with the requirement for this achievement is simple enough:
"Own 50 Character Skins"
Character Skins can be unlocked via the "Tour of Duty" as well as bought in the Store. These come in a variety of different rarities:
Common - 1,000 Coins to Purchase
Rare - 2,000 Coins to Purchase
Epic - 4,000 Coins to Purchase
Legendary - 10,000 Coins to Purchase
Heroic - 40,000 Coins to Purchase
Before you go ahead and spam all them 1,000 - 2,000 Purchases, You can also stack progress for another achievement. Which is:
This specific achievement is for Purchase/Collecting 20 Epic Variety Skins. If you were to Buy 20 Epic Skins you are looking at a total of 80,000 Coins.
If you feel like you are running low on Epic Skins in the Store, Don't Fear! You can also go on to the Character Selection, pick your desired character you would like an Epic Skin for and Purchase previous Epic skins that use to be in the store.
To see how many skins you currently have unlocked, Go to the Customization menu and underneath "Characters" it will tell you:
1. How many Skins are already unlocked
2. How many Expressions are unlocked.
Hope this has helped clear things up!
MrWhite