Your Bitwalk balance includes all funds that you have with Bitwalk. This include W$ that have been generated by you and W$ that have been transferred to your account.
To access your balance swipe to the right the Today screen.
Below your W$ balance, you can see your balance exchange value in local currency (USD, GBP, etc). To change the local currency go to Menu / Settings / Default Currency.
You cannot have a negative W$ balance.
From the balance screen you can make W$ transactions (Send / Request) by tapping on the transactions icon.