Once you’ve drawn a line or connector you’ll notice a characteristic about each endpoint: if it’s a connector with more than two segments, each middle segment has a little circle. These circles work like the squares around the boundary boxes of shapes. If you click and drag on one of the circles, you’ll only adjust that segment of the line/connector. If you click anywhere else, you’ll move the whole line.
Frequently, you’ll want to connect the end of a line to a shape so that if the shape moves, the line will stick to the shape. When you select a line, you’ll see that all the shapes in your diagram become flanked with little ‘ + ‘ symbols. There should be one in the middle of each shape as well. These ‘ + ‘ symbols are standard connection points. If you drag the endpoint of a line or connector to one, you’ll see the little circle turn green. That indicates the line is locked to the connection point. From then on, if you move the shape, the line will remain connected.
When initially drawing a line or connector, you can start off on a connection point—if the connection point shows a green circle, your line will be locked to it.