The Quarantine section shows a list of traffic sources (i.e., sources of incoming requests) that are currently banned, blacklisted, and whitelisted.
A traffic source is banned automatically when it violates a Dynamic Rule. You cannot manually ban a requestor.
However, you can accomplish the same effect by blacklisting the requestor. Instructions are here.
You can manually remove a requestor from the Banlist or Blacklist. Instructions are here.
Whitelisting a traffic source will make it exempt from Dynamic Rules. Instructions are here.