The horizontal axis represents the days
The vertical axis represents the amount of money in the wallet
The first part is a horizontal line which means the amount of money on the first day is the same as the initial amount
Let us say, you have some money in your wallet, and you went out to buy a shirt on the first day but you did not find a suitable one, so the money is still the same in your wallet.
The next day you went to buy some groceries, from the supermarket, then you went to buy a shirt from a shop, finally, you drank a coffee in a cafe, so the money in your wallet is decreased.
The next day you paid the rent cost of your house which made your money become nearest to zero. So you decided to stay at home because you had a little amount of money
The next day you went to your bank and take an amount of money to raise your amount in your wallet and stay with this amount for a while.