For a new QVTr file the editor should open up showing
The example uses the leftMM and rightMM meta-models, neither of which exist, so these contribute the first two errors. These are presumed to supply the Left and Right classes, whose absence produces two further problems.
From the Eclipse main menu (or project right button menu) invoke File->New->Other...
Select Example EMF Model Creation Wizards->Ecore Model then Next
Select your project (Temp) as the container and Left.ecore as the file then Finish.
Within the editor for Left.ecore, select Show Properties View
(from the right button menu).
Rename the root package to left (from null), by opening the root resource to
show the null package, selecting it and changing its Name to left (in the Properties
View).
Create the Left class, by invoking New Child->EClass from the right button menu
of the left package. Specify its Name as Left in the Properties View.
Save and close left.ecore.
Invoke UMLX Natures->Add Model Registry Nature from the right button menu of your project (Temp), so that the project has a Model Registry Property Page.
Invoke Properties, Model Registry from the right button menu of your project (Temp) to open up the Model Registry Property Page.
In the Property Page for the Model Name Accessor, invoke New...
Enter leftMM, and use Browse Workspace... to locate left.ecore.
Hit OK and OK to complete the registration.
The errors associated with the leftMM should now disappear.
You may repeat for the rightMM, but by now you are probably ready to use your own models.