Here's an example race for selection:

Sat May 7 at SR Canterbury
Race 3 De Bertoli Wines Hcp 1100m 3yo & up Benchmark 85

1. 04850 Mount Verde 59.5k 21.00
2. 70871 Empire Place 57k 13.00
3. s5549 My Vegas 57k 13.00
4. s070s Martin Place 56.5k 35.00
5. 02471 Fitness Fanatic 56k 5.00
6. 1s211 Rain affair 56k 1.42
7. 32107 Mighty Obvious 54k 35.00
8. 33012 Ravna Gora SCRATCHED
9. 30s00 Danza Doll 53k 23.00

So I rank the top 6 using the odds on the right.
1st Fav would be #6 because the odds are 1.42
2nd Fav is #5 because he is 5.00
3rd Fav is #2 because 13.00 is the next odds and also #2 won his last start.
4th Fav is #3 because he is also 13.00 but with worse last start result than #2
5th Fav is #1 at 21.00
6th Fav is #9 at 23.00

To bet on the race, the 3rd Fav needs to be equal to or greater than 6.00, the 4th >= 8.00 and 5th >= 10.00. This race qualifies and so my selections would be #2, #3 and #1. They then go into my staking plan with weighs them based on their odds to make sure that whichever horse wins, a similar return on investment is achieved with an outlay of around 10-12 units per race. Sometimes the return is higher, sometimes lower than expected. In this case they were staked 4, 4 and 3 in that order, for an outlay of 11 units.

In this case the 1st Fav won. No problem. If the 3rd Fav had won at 13.00 then I would have won 52 units for an outlay of 11.