There are two ways to mark a waypoint.
1. If you do not want a picture file with the waypoint, do not turn on Snapshot in the Accessory menu. Then it makes no difference if you are at a place you want to mark a waypoint or if you move the map curser to a place on the map. You quickly push the MARK button and you get a WP waypoint. You can have Navionics, Lakemaster, or just the internal map and do that.
2. If you want a picture file with the waypoint, you turn on Snapshot in the Accessory menu. Then it still makes no difference if you are at a place you want to mark a waypoint or if you move the map curser to a place on the map. You have to push and hold the MARK button for a couple of seconds to get a S waypoint with the camera icon. If you quickly push the MARK button, you just get a WP waypoint and no snapshot.
You can EDIT the S waypoint icon to whatever you want. It does not have to stay the camera icon. The waypoint name will still be S---- unless you edit that also.
Another thing, a waypoint is not a map feature, it is a GPS feature. A waypoint is written to the unit's memory and will be displayed on whatever map background you use. It is not written to a map card.