How do I add a text label onto an arrow line?

Question

I want to add a text label to an arrow line

Answer 1

Right-click the edge (i.e. what you call "arrow line") to open its context menu and choose "Add Label".

Alternatively, left-click the edge to select it, then press F2. If the edge already has a label, F2 will open the text editor for the existing label. If the edge does not yet have a label, F2 will create a new label and open the text editor for the new label.