The Current value of a Holding is equal to the last Valuation (if it's automatically provided by Exirio), or the last Valuation manually inputted by you plus all Deposits and minus all Withdrawals since.
Let's take an example. If you bought a house in 2018 for $200,000, valued it in 2019 at $250,000 then today's current Value is 250,000. But if you did some renovation works in 2020 that you believe have increased its value by $25,000 (and therefore have accounted for it with a Deposit of $25,000), the current value will be $275,000.
Conversely, if you lent your cousin $50,000 two years ago and he has since given you back $10,000 (which you have accounted for with a Withdrawal of $10,000), then current Value will be equal to 40,000 USD.