When you have 30$ of gain (cash or daily interest) you can exchange them to Ethereum or Etherbanking coin.

If you choose Etherbanking coin, you can withdraw them when your profile is ok, or you can buy other lending packages (when your EBC internal wallet has minimum 100$ of value inside)

If you choose Ethereum, you can withdraw them when your profile is ok, or you can buy other lending packages paying with internal funds, or buy ICO packs with internal funds. You can add more Eth from your external wallet and invest all together too if you like.
Lending packages will give you more daily interest. ICO packs will give you only coins with a % of bonus coins (1, 3, 5, 7 or 10% more than price you buy).

Changing directly $ in EBC will give you not bonus, but you have a coin that for now can not to loose value, it can only grows up.