From the Betting exchange site’s home page, you need to go to the race that you want to bet on. This will take you to the betting screen with the prices. The odds will be constantly changing as more money is  bet on a race. Near the off of a race, the situation can quickly change with some sites, the screen will automatically change to show the new odds but with some you may need to refresh the screen to see the most up to date odds.
Betting options
You have several options:
•    to back a horse at the current odds available
•    to lay a horse at the current odds available
•    to place an order for back odds of your choice
•    to place an order for lay odds of your choice
•    to back all
•    to lay all
•    to cancel unmatched bets.

Back a horse at current odds
Suppose you want to bet £100 on a horse to win at odds of 2.0 and these odds are available, you place your bet by clicking on the box containing these odds. You will be taken to a screen that is the equivalent of a betting slip. This screen will show the odds and will prompt you to enter your stake. You will then be taken to another screen to confirm your bet.

You have the option of cancelling your bet as long as it is not matched. If just a portion of your bet has been matched, you also have the option of cancelling the unmatched portion.  Once a bet has been fully matched it can no longer be cancelled. If the  horse wins, you will win £200 less commission. If the horse looses, you will loose £100.

Lay a horse at current odds
Suppose you want to lay £100 on a horse to lose. Lay odds of 2.5 are offered and there is £500 unmatched. In order to place a bet, you place click on t?e box containing these odds. You will be taken to a screen that is the equivalent of a betting slip. This screen will show the odds and will prompt you to enter the stake. You need to enter the backer’s stake that you are willing to match. You enter £100. Your liability is £150 and will be displayed on the screen. The liability of £150 is how much you will loose if the horse wins. The stake of £100 will be how much you will win from the backer if the horse loses.

Calculating your liability
To calculate your liability you need to deduct one from the decimal price and multiply the remainder by the backer’s stake. Lets say the decimal price is 2.5. The backer’s stake is £100:
2.5 - 1 = 1.5
1.5 X 100 = 150
liability = £150
Calculating commission
The betting exchange charges commisson for its services. Commission is typically paid on net winnings at a rate of around 5 per cent. This compares favourably to a traditional bookmaker where a charge of around 10 to 20 per cent is made.

Example
You back £100 at 5 and win. Your returns are £500. Your stake is £100. Net profit is 500 - 100 = £400.
Commission = 400 x 5% = £20
Profit after commission = 400 - 20 = £380
Returns = 380 + 100 = £480
You lay £100 at 5 and win. Your returns are £100. Your stake is £400. Your returns are £500. Net profit is 500 - 400 = £100.
Commission = 100 x 5% = £5
Profit after commission = 100 - 5 = £95
Returns = 95 + 400 = £495
Book percentage
The book percentage or over-round tells you how profitable a book is. The book percentage is shown for the back and lay markets. It shows how competitive the prices on offer are. It is calculated by adding the individual percentage chance of each selection based on the price that it’s being offered.  A book that is perfectly balanced will have a percentage of 100 percent. In this case both backers and layers would break even. If you are laying all selections in a market (like a traditional bookmaker) you should ensure your book percentage is greater than 100 per cent, then you are guaranteed to make a profit. If the book percentage is lower than 100 per cent you will lose money.

If you place bets with a book percentage greater than 100 per cent, and all your bets are matched, you will make money.
If you are backing a selection, you would ideally look for a market where the book percentage was as low as possible, that is as close as possible to 100 per cent. Occasionally a book percentage will go lower than 100 per cent (overbroke). In theory, you could then back every selection and guarantee a profit.