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

The goal isn’t to replace gmaps, though? If it was, I don’t think they would care to allow me to map the species of tree of the height of a curb. Some apps are trying to use OSM as a base layer to provide a gmaps alternative, but the real goal is just to map the world, at least to me

That’s the best part about OSM, if it’s lacking in your area, it’s super easy to fix yourself! iD, the editor built into openstreetmap.org, is super easy to use, or an app I started using a lot more recently is StreetComplete, which lets you answer simple questions as you walk around