Ozone is a plugin
It is marketed as a mastering plug so the idea would be to put it as an insert on the master bus although you can use it at the track or sub mix level
Presets are a starting point, They are one persons opinion of what processing should occur but they were not designed with your specific music in mind, in fact the person who made them never hearrd the track you are working on so how the eq, compression etc could be "right" for your music is a total stab in the dark, a complete one in a million chance it will be what you actually need. It will not magically make your music great.
Ozone should be used with great care it's very easy to ruin a perfectly good mix with it and using presets is about the fastest way to do that