You start at your cable box and find the in and the out scarts - in is usuakky labelled IN and out usually labelled TV. Stick a scart lead in the TV Scart of your cable box with the other end going into your VCR's IN scart socket.
Then run another scart lead from your TV or OUT scart socket of the VCR to one of the scarts on the TV. This allows you video tape anything on cable onto your VCR and watch it too.
Then connect a scart lead to the OUT/TV scart socket of your DVD player and connect it to one of the other Scart sockets on your TV.
Finally you can connect your cable box straight to the other scart socket on your TV using the existing sockets - this lets you watch cable directly from the cable box.
You then need to press the AV button on your TV remote to watch the respective VCR/Cable/DVD inputs.
Hope this helps.