Mandalorians come from the planet Mandalore. They are a society of warriors who helped fight the Jedi in the Old Republic. During the Clone Wars era they were mainly pacifists but a group of “Terrorists” know as Death Watch(which Darth Maul helped lead) tried to restore their fighting ways. Obi-Wan was a big player in this fight against Death Watch. The story arc takes up a lot of The Clone Wars series. I cannot recommend it enough. It also continues on into Rebels as Sabine is a Mandalorian heir.
Not sure if the show will focus on Mandalore or not. The Fett’s wore the Mandalorian armor and Jango was considered an outcast of Mandalore and was recruited by Dooku to become a bounty hunter. Later on, Boba’s armor was recovered and used by a lone renegade “sheriff” to take up the mantle. So maybe it will follow his story line?