The cash history is sort of the opposite view to coin summary, it shows your transactions from the point of view of the chosen fiat currency.
Here the blue (purple on some platform) text rows represent a valuation of some cryptocurrency that has changed hands, where as the rows with the black text are when cash / fiat currency has changed hands.
As you can see when you buy some coin (cryptocurrency) on an exchange you see a fiat currency debit (in black) followed by a cryptocurrency credit of the same value. Naturally when you sell a cryptocurrency for cash (fiat) the debit and credit will be the other way round.
You can export the result to csv or xml (this can easily be imported into excel or other accounting software) and then combined with your other taxes by your accountant or tax professional.
The transactions in the highlight color (purple or blue depending on the device) are ones that are indicative (estimated) cost because no fiat currency has been involved.
Tapping on a cashflow here will show you the break down of the transactions that created it.