Double click to create a single point. To connect two lines in JOSM find a node and begin/end your new line there. But be careful sometimes it will assume the new line belongs to the old.

To extend a line find an end point (node), select the line (Click on the line where no node is), then in add Line (same as add point) mode click on the end point and continue. JOSM assumes some things are obvious when they kinda are not.

It took me a long to to realize that two lines (areas) can sometimes share the same nodes just one on top of the other. Like when grass shares a wood line with grass on one side and wood on the other. You can hold down the key and keep clicking to see the other lines tags (in select mode). JOSM has a million tricks like that.

Want to combine two nodes into one node. Select one, hold the shift key down and select the other and type “m” (merge). etc etc etc.

A trail can have a local name and be part of a larger route. LIke a street name in town and a highway number (a name). So in town US highway 14 uses Broadway Street through town. You want both names. In town every corner might have a sign that says Broadway, but only has a sign for the US highway 14 when it changes to another street. That sort of thing.