We were all beginners once. Sometimes you don't even know where to start. If you've never decorated with a pastry bag before then you may not know how to fit your tips and tubes correctly. Measure twice, cut once.
There seems to be some confusion out there about couplers. We get phone calls asking...What is this hollow screw thingy for? How do I attach it? Why do I need it? Here is a quick run down on frosting tip couplers.