MWE: Many Spheres of different sizes

Create the centers and radii of the spheres

centers=RandomReal[{0,1},{20,3}]

sizes=RandomReal[{.1,.2},20]

Use MapThread to assemble them.

Graphics3D[MapThread[Sphere[#1,#2]&,{centers,sizes}]]

Color them

colors=Hue/@RandomReal[{0,.3},20]

Graphics3D[MapThread[{#3,Sphere[#1,#2]}&,{centers,sizes,colors}]]