The summary screen is a summary of various useful pieces of information concerning you current status.
Mark to market GBP
This is a spot valuation based on the current market value of your portfolio.
This is the profit or indeed loss that you would make if you were to close you position at this moment. Note this takes into account all the buy prices and quantities that comprise the opening position.
PnL to date
The profit and loss made so far for all the transactions in the app.
PnL for Period
This is during the period configured in the settings page. The profit and loss made during this time window.
Tax for Period
The tax calculation for the time window configured in the setting page. This is typically a single tax year.
PnL minus Tax
This is the PnL i.e. the money made minus the tax liability. So this would constitute the 'take home' coin you have after paying tax.