Fuse models into one STL file

Hello, I have problems using the 3d Slicer trying to export the structures to Stl as one object.

I have import two objects as Stl and link them but they don´t appear as one object.
I would like to know how I can export them as one object or fuse them as one object.

Greetings and thanks
A beginer

Hi. I have a problem.
I would like to export all the projects as an Stl.
The objects are a fusion of two cranium part that has been imported as two Stl objects.

Kind regards
A beginner

If models do not overlap then you can use “Merge models” module. If the models overlap then you can compute Boolean union operation using Combine models module - provided by Sandbox extension (you can install it using Extensions manager; the extension is in Examples category).