This is probably basic but I am a complete newbie. I searched for editing layers but am having difficulty understanding it. Here's what I have and understand so far.
I imported a KML file as a vector line. I understand I can't edit the KML import directly. I need to first save it as an ESRI shapefile. I have done that. I also toggled edit mode for the new layer and turned on the Vertex tool, which I think (not sure) is the same as the Node tool I've seen descried elsewhere - at least the icon looks the same. But then I am completely lost.
In the graphic, the magenta line is the complete track. The yellow box represents the portion I am trying to keep. I would like to delete the rest. I'm hoping this does not require a point-at-a-time deletion. For example, the segment in the yellow box from the loop on the top left to the "racetrack" at the middle right is about 9 miles. That would be a lot of points!