Ping the grid. Read the numbers. Buoy every mine.
Clear five boards before your hull gives out.
Tap a cell to ping it. A number tells you how many mines touch that cell. Your first ping on every board is always safe, and every board can be solved by logic alone.
Switch to Buoy to mark mines (or right-click, or press and hold). Tap a number whose mines are all buoyed to clear around it.
Hitting a mine costs 1 hull point and the board carries on. Lose them all and the run is over.