It's all in the help guide, and is very easy. You've got 3 types of nodes, and tubes connecting them together. Fundamental nodes go on the ground (footers), Track nodes attach to the track, and Free nodes can go anywhere. When you have your nodes in place, choose the type of tube you want to connect them with then drag a line between them. Easy as pie. (you have to be in support mode for this).
-Ride_Op
-----------------
NoLimits Tournament of Champions now underway at Ride_Op Coaster Productions! http://rideop.twistedrails.com