What is a betting exchange and why do I need to use one?
A betting exchange is a place where you can bet both on and against a result happening. With matched betting, the main focus is on the against part as we use this to ensure all outcomes are covered.
The best thing about the against bet is it allows us to bet on, for example, a team to win at the bookie side, and bet against them winning at the exchange. It covers all outcomes with just 2 bets! Normally you'd have to bet on the Win, Draw & Loss.

Without exchanges, Matched Betting wouldn't be as profitable as what it is! They really are a Matched Bettors best friend!
Key Terms
Stake - Unlike with bookies, the stake is NOT what you are risking, it is you saying what you want to get returned
Liability - The liability is the figure that is calculated once you enter your stake. This is the amount you have to risk.
This confused me at first because I was so used to stake being what you place and then get offered a return.
The easiest way I got my head around it was to just remember its the complete opposite.
With bookies you tell them what you want to risk(stake), they will tell you what they are willing to risk in return(liability/return).
With exchanges you tell them what you want to win(stake), they tell you what you will have to risk (liability)
I hope that is clear enough. It is confusing at first I wont lie!