GC does not accept deposits and withdrawals directly through banks. Hence, you can deposit your currency to Top Change from your bank account and transfer the amount to Green Change.
If you want to buy Tether, you do not need to do anything else as the mentioned transfer is to the GC Tether wallet.
If you would like to buy any other currency, you can do so through the "Convert" option;
Dashboard > Quick Access > Convert (Steps shown in the link below)