Erik Kostson
Ansys Employee

First, I would step back and recommend to take a course in the use of SpaceClaim:
The above course is a good start before proceeding with the part mentioned here next.

Once you are confident with the basics in SC, try this part.
So start a new model, and do like in the video and as shown for the first 25 seconds in the video. 1. So define the cross section (sketch), which in the video is a square section (you would need to sketch your section, say tube or I, whatever it is), and then finally extrude it (sketch of section) into a 3D part.

When you have all members defined as Peter said you will need to use Split Body to construct the intersection between the two tubes. Use the Prepare tab and click the Share button to create the weld line.