... Read the
Wiki. You are actually encouraged to do that if you need a ratio boost.
Quick explanation on the public tracker, though, as I don't think it's covered...
The tracker resets its public key every month. If you happen to be downloading the public torrent with the BakaBT tracker not listing the current month, you will not be able to download from BakaBT's seeders.
If you are, however, lucky enough to get a public torrent with a tracker key that is still valid... That's pretty much self-explanatory.
And yes, once you switch over to the private tracker, your stats begin being recorded. Note, though, that it's easier to just download the torrent from BBT, so you don't have to change DHT to not allowed, etc.
You can get a public key yourself without having to find them on third party sites, but how to do that is plastered everywhere on this forum, and may or may not be covered in the Wiki.