Question ! , how do you make a model rotate on it's side ?

I want to make a fan that are 8 blades that are grouped together into a model , I already know that you should use :SetPrimaryPartCFrame() to a invisible primary part , and did while do true() to make it loop forever . but i don't really know what next i should do ? , Im pretty confused on this part , if anybody could give me an example or explain it to make then i'd appreciate it

PS : The Fan is moving endlessly, Script the i have wrotten :

Fan = script.Parent
while true do
    wait()
    Fan:SetPrimaryPartCFrame()(Fan:GetPrimaryPartCFrame())
end