EVE PLEX can be traded or sold between players on the in game market. It can also be used in the New Eden Store to upgrade your account to get Omega Clone state, purchase virtual goods, and activate other account services.
15400 PLEX is valued at $0.03246 Cents each. This is the BEST VALUE PLEX package there is. This has the lowest cost per and will yield you the highest return per dollar in game. Funding your Corp or just funding yourself you can't go wrong with this mega PLEX package.
To use PLEX in the New Eden Store, It must be placed in your PLEX Vault. The Vault is a secure location in your inventory, shared across all characters on your account, where it can be placed for use in the New Eden Store. You can find the Vault in your inventory in the Neocom (Upper left corner of your game screen).