There is a great explanation is this thread http://forums.cardhunter.com/threads/new-player-faq.7451/
Please read the FAQ: http://forums.cardhunter.com/threads/comprehensive-card-hunter-faq-and-glossary.6913/
http://forums.cardhunter.com/threads/new-player-faq.7451/ http://www.cardhunter.com/2015/07/ganging-up-on-gary-cooperative-card-hunter/