Sailing shows the boats heeling (1), heading (2) and current speed as provided by the gps of your phone.
To change units between metric, nautic and scientific see: Settings.
By a long tap at the heeling field (1) you can set the upright position of the display.
At the bottom your current position is show (4). To share your position long tap at the field, the phones share view will appear.
Here you may also open your current position with Google Maps if installed.
At the bottom's right side the gps accuracy in meters is shown (5). If the accuracy is less than 6 m it is probably insuffisant for nagivation and shown in read as a warning.
In case of bad gps accuracy the app tries to smooth the values for speed and heading to prevent from heavy jumping of the values.
A long press on speed (3) or heading (2) makes a popup menu appear that lets you configure this view:
(1-2) Switch the views for heeling and heading on or off. Speed is always on.
(3) Night mode, display turns to red.
(4) Speech output of your current speed, set the frequency.
(5) Speech output of your current course, set the frequency.
Don't forget to confirm your choice.