If I create a stroke with , and I want to join an end node of another stroke, also made with How do I do it? I use the node selector , select the nodes, and click the "Join Nodes" command, and it never works.
The only promblem is, one node is usually and "end" node, while the other node I'm trying to join it to are in the middle of the stroke path somewhere. Can't this be done? Seems like a basic function, what am I missing?

It can't be done unfortuntely. It's discussed briefly in the frequently asked questions.

If you want two nodes at the same spot, I would advise turning on the snapping functions and use the different stroke style caps to make the lines join smoothly. If you later want to move the nodes, you can select both nodes simultaneously by click-dragging around them when in the node tool . It will look like you only have one node highlighted, but if you try moving it you will notice that both nodes will follow your movements. Note that in order for this to work if the nodes are on separate objects, both of the objects need to be selected.