A pebs is the currency from LinkFed, they're analogous to the karma point system from reddit or hackernews. They're based on the
Science Fiction series The Monk and the Robot by Rebecca Chambers.
If you have pebs you can use them to ask for help in LinkFed or show appreciation to people and commenters. They're kinda like a virtual kudos card. It's a shown of appreciation on helping maintaining this community and things floating around.
You can get pebs by helping people on the ask section, commenting and creating post. Nurturing the community and teaching others. If you're technically proficient you can also get pebs by programming LinkFed, maintaining the server running or translating the website. Everyone is part of it.
Nothing much really. Even if you don't have pebs you can ask questions or ask for help. We don't let anyone behind. Now, people who follow you or admins can see that you're into the negative pebs and check if you need some help. It's normal, sometimes we're in a bad season.
You can't really be banned if you're in the negatives pebs but if you break the rules or get reported too many times you will be banned.