For segmenting, take a look here:
Even though you may have some experience on other sites, it is obligated to go through the NSSA before you can start segmenting.
If you want, you can be in a subbing team too, even though you only speak English. If your English skills are good enough, you could be a GE (General Editor), someone who checks and edits the English subtitles of a show.
You cannot mess something up, cause you won’t have access to a show until either the CM (Channel Manager) or a moderator adds you.
If there is a show you want to work on, you can ask them. But in most cases they will only let you work on older shows and as said, for segmenting you need to go through NSSA first.