mogulfield - you just need a free bet with the bookie in order to make money. At the exchange you are acting as the bookie so you're not likely to get free bets there (and if you did you'd have to lay the bets at another exchange). So. The basic principle is as follows for all these bets:
Bet £5 get a £10 free bet. (for example)
Bet £5 at the bookies at the minimum qualifying odds. You lay this bet at the exchange either by finding the best qualifying bet through Odds Monkey (or whichever site you're using) aiming to lose the least amount of money possible (ie using low odds). For this you are using your own money.
Once that bet is settled you get your £10 free bet. This is free money at the bookies which you'll find a bet which gives you the most profit. (again using the oddsmatcher calculator or finding it yourself and using higher odds). You'll still need your own money to cover the liability at the exchange but the profit will be yours either way as you have a free £10 to make the bet.
So, each profitable bet is actually the result of a qualifying back/lay bet and a free back/lay bet - four bets in total.
It sounds horrifyingly complicated when you first start but it soon becomes second nature - promise!
but don't ask me about accas or anything more complicated as I haven't a clue 