The oddsmatcher explained

Click anywhere on the event of your choice and an additional screen will supply you with more information.

In addition to the time and date of the actual game involved and the particular selection which you'll need to Back bet and Lay bet on (SHEFFIELD UTD TO WIN), you will also see that this is a Championship fixture and that the market is for "Match Odds". You can see the actual odds at each company and you'll also notice some cash information under the pink Lay button. This tells us there was £339 liquidity at odds of 2.41 available at the Betdaq market (4 minutes ago). The more the merrier is the rule here, but as long as there is more than you are looking to place, everything is good. Finally, note the Open Calculator option at the bottom (more later) and the direct links to each site in question, which in most cases will take you straight to the relevant screens at each company, minimising the amount of time it takes to find the market in question.
 

The best thing to do at this stage is go and join a bookie and betting exchange of your choice. Have a look at the review pages and take your pick from the banner links which will take you straight to the relevant promotion pages. We recommend the smaller deals first to build up your funds or some of the more well known companies if your still feeling nervous about betting (not gambling) - maybe William Hill (£25 free bet), Skybet (£10 free bet NB AS OF 8.5.10 SKYBET IS NOT CURRENTLY OFFERING THIS FREE BET. OUR SUGGESTION IS TO USE CORAL - SEE LINK BELOW) or Betfred (£50 free bet) depending on how big a deal you want to take advantage of. By joining the companies before you ultimately choose which events to bet on, you will give yourself more time to complete the bets (the joining process can take a few minutes and it's possible that during this time, the odds or the liquidity on offer may change).

When it comes to the exchanges, Betfair and Betdaq are also offering free bet deals. You will need to join at least one of these companies to place your lay bets with (you'll lay bet here every time you back bet at a bookie). Betfair is the biggest and best, but currently their free bet offer is only available if you lose your first bet (N.B ALL THE OTHER FREE BET DEALS AT THE BOOKIES DO NOT HAVE THIS "IF YOU LOSE" CONDITION). It's probably best not to concern yourself with trying to obtain this free bet at Betfair on your first go - if you do happen to win at the bookie and lose at Betfair, consider it a bonus. To give yourself the best possible chance, go for a low odds first bet at a bookie like William Hill, where there are no minimum odds for your qualifying bet. Chances are the low odds bet will win (as you're betting on the favourite it's probable but not certain) and the lay will lose, so not only will you qualify for the free bet at the bookie, you'll also get the free bet at Betfair. Double bonus! 

After you have joined a bookie and an exchange come back here for help in finding and placing those bets.

Now to Step 5.