Initial balance

Choose Transactions on the top menu, then Add (or use the Add icon to add transaction). Choose Income and enter a positive number for your opening balance. Maybe add a Memo to note this is the initial deposit.

As an alternative to Income, you can choose Transfer if the funds for the initial deposit are taken from another account that you have entered into HomeBank.

Or, you could select Manage->Accounts then, from the list in the left column select <your account>.
In the right column select the General tab.
Now simply enter the value in the field 'Start balance'.
press Close button.
Back on main screen, click on the dark blue Save button and you are done !