Using map or compass hit the mark button. Select waypoint. Enter a name for the waypoint or leave the default. From this popup screen you can enter a lat/lon using the coordinate system from your settings.
Alternatively, you can export your coordinates as GPX and import them into a trip on the web site using the trip panning feature. Once you have saved your trip on the web go to trips and guides on the phone – the trip you created on the web will be moved to your phone.