Hi @davidullman Welcome to the Forum
There are so many ways to achieve your objective within S3D, the following may help
Bear in mind these are a guide only, choose the actual shapes required:
Sketch your Design and Copy:
Alter the view and Select the Shape(s) to be Pulled or Pushed
In both cases both Shapes were Selected the left by 30mm and the right by 20mm:
Next the 'T’on the left was Pushed down and the ‘T’ on the right Pulled up:
To get the ‘fit’ needed Pull or Push individual Faces in the appropriate direction
While the Measurement/Dimension Figures are visible click on them and alter to requirement in the Pop Up as shown above.
Just shout if you need more help, the Beginners Tutorials accessible from the ? top left menu is great place to start.