Cost basis is what you paid for the holdings you own today, plus the cash you hold. Take it away from the portfolio value and what's left is your unrealized gain, the profit on positions you haven't sold yet.
Cash counts at its balance, because a euro in your account cost a euro. When you sell at a profit, the gain is counted once, in Realized Return, and the money from the sale simply becomes part of your cash.
In the metrics table, Initial Balance is what your holdings cost and Current Balance is what they're worth now. Add Cash to each and you get the cost basis and the portfolio value.
Net invested, in the cost basis tooltip, is what you spent buying positions minus what you got back selling them. Cash isn't part of it.
Total Return is everything you've made: realized and unrealized gains plus dividends. Capital Return is the same figure without the dividends.