Is also referred as 'on the nose', and it means that you're selecting a horse to win. This is as per the example above about Monty's Pass.
Also remember that your winnings are tax free.
For the Grand National it is probably a good idea to place each way bets, as the odds of the horses are generally quite attractive - and in excess of 10/1.
Betting exchanges are slightly different to bookmakers, as you are betting against other punters. The odds that are offered tend to be higher, though if your bet is a winning one, you would be charged a commission on your winnings. With place-only betting, you usually find that another individual is prepared to offer higher odds than the bookmakers - so it may be worth keeping in mind if you want to place this particular bet.