There are 4 exchanges, only two of which most people use. They are Betfair, WBX, BetDaq and Smarkets. At any of these you can place a back bet or lay bet. You are betting against another punter and the exchange make their money by charging a commission to the winner of the bet.
Every other bookie is just that, a bookie. They only accept bets, they in effect are laying your bet. You cannot lay a bet yourself with a bookie
"All you need to ask yourself is do you feel lucky? Well do you......Punk!"