QGIS - Unable to Create New Shapefile

I am running Windows 7, QGIS 3.12.3 Bucuresti and hitting a wall trying to create a new shapefile. I have georeferenced (GeoTIFF) imagery and I want to create polygons that cover forested areas within the imagery in order to assign a particular forest type (coniferous, deciduous, etc.) in an area in Eastern U.S. This will be used to import into FlightGear as new Scenery that will populate the tree(s) into the scenery. I ran across a "How To" article (http://wiki.flightgear.org/Howto:Create_custom_terrain) that appeared to cover what I want to do, but I believe it’s based on a very, very old version of QGIS (1.X).

I may be approaching this wrong, but I select Create New Shapefile Layer, give it a unique name, select Polygon, and add a new field called "Class" (Text Data) and add it to the Fields List. With both the respective imagery and the just-created Shapefile in the Layers window (made sure that the CRS was the same in both), I left click on the Shapefile, then right-click, select Toggle Editing, then draw the polygon on the visible imagery. I believe that after the last point is selected, I should "right click" and the polygon should remain visible. However, nothing happens. However, if I select the Imagery file, then do the same, the polygon disappears and I get the following error: "No active vector layer: To select features, choose a vector layer in the layers panel." In the instructions in the above "How To", it never mentioned creating a Vector layer.

Any info, or a pointer to a more up to date tutorial?