Your account level (your level in the game) is dependent on your lures and their levels.
Upgrading a lure will give you experience points. The rarer the upgraded lure is, the more experience points you receive. After obtaining a certain number of experience points, your account will automatically be leveled up.
Leveling up will open new fisheries for you. For further details on new areas to fish in, please check the How to unlock a new fishery? article.