The ordinary world for Killmonger is a small poor neighborhood with his father. He was surrounded by dangers and unfairness.
Killmonger's call to adventure was when his father was killed by Wakandians. He knew all about Wakanda and the Vibranium and had always wanted to go there. After his father was killed when he was young he wanted to go to Wakanda and he wanted to share the vibranium with the world.
Killmonger meets his mentor he he teams up with klaw to steal a vibranium powered weapon from a museum.
Killmonger crossed the the threshold when he killed Klaw and brought him back to Wakanda after his cousin, T'challa failed to kill him previously.