I don’t know what OsmAnd looked like at the time of Organic Maps being started, but IMO based on how they look, OM is much more welcoming to the average user and OsmAnd is for power users. I still keep both on my phone, but I reach for OM first nearly everytime

The simplest way is to trace it on the starllite imagery available on the editor built-in to osm.org. If it’s not visible there, here is the wiki’s list of Android apps that can record GPS tracks, and it’s not hard to find the other pages on the wiki about getting those off your phone and into the map. Some of those apps can probably do that bit for you, I’ve just never tried