Let me also give an "expert tip" to remember the MICE keys. When you are placing or modifying objects you can hit the keys on the keyboard to get that keypoint M=Midpoint E = Endpoint, you get the idea.
So when placing a line and you want to connect to the midpoint of another line, just hover over it and hit the M key --> Voila!
This works with the connect constraint as well. Choose the connect command. Hover over line one and hit M. Hover over line 2 and hit E and.....
Dan Staples Director, Solid Edge Product Development