The only way you can understand and get value is if you give prices to your rated horses.

You might rate a horse 80% chance of winning which is odds of roughly (100/80) = $1.25

If you can find odds higher than $1.25 you are getting value. This means that even a horse paying $1.30 might be good value.

Without working out your own rated prices there is no chance of knowing what is and what is not value. For instance your top rated selection might have a 25% chance. This works out to be $4.00. You might only be able to get $3.80 so this horse has no value.

Hope that clears it up.