you did an each way bet?
10p each way is 10p for a win and 10p for a place, therefore 20p.
if your horse got placed (2nd, 3rd or 4th depending on the amount of runners) you will get 1/4 or 1/5 of the odds (depending again on the race), ie the Starting Price. plus your stake money back.
so, it seems you did a 10p each way bet on a horse with odds of about 2-1.
it didn't win but got placed, so a quarter of 2-1 is 1/2-1. so your stake money for the place, (you lost the stake money for the win), plus your 1/2 returns, the 5p.
highland will prob explain this in about 2 lines....