There are an awful lot of ways and things you can use to strop a kitchen knife, and I've probably tried most of them. Different people like different things, but here's a very short video showing what is probably the easiest and actually still my favourite way to do it: Any kind of paper or card, as long as it's not shiny, is excellent for knife stropping.
In the picture below that you can see the black line on the newspaper of oil and swarf that was on the knife before, and which shows where I've been stropping, i.e. where the paper is folded over the work surface. I don't have the knife laid flat on the newspaper to strop large sections of the edge at the same time (though of course - there's nowt wrong with doing that either if that's what works for you!)
In the picture below that you can see the black line on the newspaper of oil and swarf that was on the knife before, and which shows where I've been stropping, i.e. where the paper is folded over the work surface. I don't have the knife laid flat on the newspaper to strop large sections of the edge at the same time (though of course - there's nowt wrong with doing that either if that's what works for you!)