There are two ways to add text to your draw.io connectors. The easiest way is to select the connector and just start typing. If you want the text to start from a specific position, double-click on the connector at the point where you want the text to be, then start typing. Of course, your connector texts can be formatted just as texts in shapes, using the Format panel. To reposition texts, grab the orange diamond and drag it to relocate the text.