How to add new Trackers?

[KrKing12138]

I have some new trackers, for example, udp://tracker.opentrackr.org:1337/announce
How can I add it to my Cloud Torrent service?

By the way, I'd like to know how many trackers are used exactly when downloading one file? One or more?

And, can I choose some files to download but not all files in a torrent? If it's possible, please tell me how, thank you!