3M cerium belt or disc

[Havi]

I need to polish the piece I have working on, and nagging you lately.....................

I have many tools that I can use [WBS, flat bed grinder and angle grinder], I have felt and I have those 3M cerium discs, which are supposed to do the polishing too... [the white discs]

I do not know how it should work, never succeeded with it.
Do I have to add the cerium powder?
If not - how does it work?

Anyone had real success with this?

I'd be grateful for your imput,

Havi