What do total lines at the bottom of the main screen show?

The first total line is about expenses and it shows total bill amount (Bills), total paid amount (Paid) and outstanding bill amount as O/S stands for outstanding.

The second line is more about for giving an overwiew of the current period. It shows total income (Income), total bill amount (Expense), which includes all paid and unpaid bills, and the balance (Balance) which is (total income - total bill amount).