GeoGebra has two tools that can be used to draw spheres in 3D-space: 
If you want to draw an arbitrary sphere, choose Item 4.
If you know the radius and center of your sphere, choose Item 4.
     GeoGebra Instruction 1
Sphere: Center & Point Tool Algebra     View     and         3D     Graphics     under         View     in         Menu.         Sphere:     Center     &     Point 3D     Graphics.         This         point         will         be         the         center         of         the         sphere.              GeoGebra Instruction 2
Sphere: Center & Radius Tool Algebra     View     and         3D     Graphics     under         View     in         Menu.         Sphere:     Center     &     Radius 3D     Graphics.         This         point         will         be         the         center         of         the         sphere.         GeoGebra     will         now         ask         you         to         type         in         the         radius         of         the         sphere.         Type         in         the         desired         radius.         The         sphere         will         then         appear         in         3D     Graphics.         Alternatively, you can type
Sphere(Point, Radius)
in Algebra View, inputting the coordinates of the center of the sphere in the Point field, and the radius of the sphere in the Radius field.  
Example 1
Draw a sphere with its center at (1, 3, 2) and a radius of 2.
Follow Item 4 for this exercise. Type
Sphere(Point, Radius)
in Algebra View. Then type the relevant values into the fields where they belong. The sphere will now appear in 3D Graphics.