What are the things called that you sit on a gas stove overtop of the burner that your pans sit on top of? and how do i clean them

Would it be called a "trivet"

gas rings. you can buy special cleaner for them from John Lewis for example

There's a powder called Barkeeper's Friend, which you mix to a paste (or dab on a damp cloth). It's very good, easy to use and not chemically savage. I use it for all sorts of cleaning jobs.The pot stands on my hob are enamelled, and it works on them fine.

thanks how do you clean them??

soak them in soapy water for a few hours and then clean them with a brillo pad

I think they are called Pan-Stands, they need to soak for a few hours in soapy water or you can use hot water and washing powder. As webtrawler said you can use a brillo pad or if they are cast iron you can use a wire brush.

Pot stands - put in dishwasher if you have one.
If not put some caustic soda in the bath, add hot water to cover the pan stands and let them soak for a few hours
Quick rub down afterwards and all dirt and grime should be removed.

thanks everyone for you swift replies will try with caustic soda as soapy water has not worked thanks again:)