You can use the Sphere Tool to create spheres. When the Sphere Tool is clicked, a "Primitives" window will appear in the same space as the Group List window. Use the X, Y and Z entrants to modify the sphere's position. Use the radius entrant to modify the radius of the sphere. Any changes made in the Primitives window will be previewed in the 3D Viewing Window by a transparent gray sphere.
You can also use the controls on the previewed sphere in the 3D Viewing Window to edit the sphere. Press add when you are finished editing the sphere to add it to your existing geometry.
