a) Find 'Export' in 'Files'. You will get a pop-up:
You can choose to export your object in STL, PNG or:
- .gltf v2
- .gltf v2 (binary)
b) What happens if I try to export two or more objects at the same time?
What should happen is: you'll get a zip file with an stl or the extension you chose of every object you exported.
If you want to export your group as one object, you need to Group them. There's however a danger that this will merge them, once you import them in another 3D modeling program.