how to fit a light?

Typically...

When you look at a ceiling rose you often see two black wires joined together in a terminal block - another terminal block strip with three red wires - and a third terminal strip with just one black wire - and this single black wire often has a little red sleeve on it - or rather it should have a red sleeve on it.

The Lamp connects on one side to the single black wire and on the other side to the two black wires.

Your description appears to be a couple of wires short from what one usually finds - perhaps an electrician should be called.

Here's a diagram picture...

http://www.flameport.com/electric/lighting_circuits/lighting_ceiling_rose_other_colours.cs4

Take care...

Peccavi
July 2010