How do i add collision to a model which the player is controlling?

while wait() do
local w = UserInputService:IsKeyDown(Enum.KeyCode.W)

if w then 
    print("W was held down")
     model = game.Workspace.Model
model.PrimaryPart.CFrame = CFrame.new(model.PrimaryPart.Position + Vector3.new(0,0,-2))





else

    print("W was not")

end

    local model = game.Workspace.Model
    model.PrimaryPart.CFrame = CFrame.new(model.PrimaryPart.Position)
end 

The script works fine, but the model doesn't seem to collide with anything.

I turned CanCollide to true in everything in the model.