I have been watching many FMC tutorials about PMDG 737 and I understood most of it but still in connecting legs I have some problems. I tried using FSCommander forr creating PMDG compatible routes but I still have problems with disconnected legs. Can anyone help me to finally understand it? Is there a way that we can fly the plane together? If not, can someone try using teamviewer to show me the solution to my problems?

Try inserting the plan on your own, without loading a flight plan file (COROUTE) generated by another program.  Both tutorials show you how to do this.  The reason I say this is so that your understanding of routing has a huge impact on how you view routes handed to you (by FlightAware or FSCommander).  There are two links in my signature to show you how to route yourself, if you're interested.

 

Disconnected legs are not always a problem.  As an example, if there is a vectored portion of a departure/arrival, it will show up as a disconnected leg.  This should be left in the route.  When the controller tells you to proceed direct to [some fix], go to the FMC legs page, line select the fix, and then place it at the top, using the top left line select key.