Overview
To track the incomes and expenses, you need to assign a category to your transactions[1].
Important
Reports are valued in your currency (and not in ZEC). The currency is chosen in the Settings page; it is USD by default.
Therefore you also need to have the price of 1 ZEC at the time of the transaction.
When you make a payment, the price shown in the "Send" form is recorded with the transaction. When you receive ZEC, the transaction has no price ("N/A") until you fetch it.
Fetching Tx Prices
For convenience, the market prices can be retrieved from CoinGecko for the past year[2]. Choose "Fetch Tx Prices" in the account page menu: every transaction of the account that has no price gets the market price of its time.