Stephan Kesting teaches a simple 4-step armbar escape called the Bread and Butter Escape.
Rob Biernacki shows how to apply a super-tight armbar from mount.
Giancarlo Bodoni explains how to do a proper Armbar from closed guard.
These are the first five submissions you should learn in Jiu-Jitsu. The submissions include the Americana Armlock/Ude Garami, Straight Arm Lock/Juji Gatame, Kimura Armlock/Ude Garami, Guillotine Choke/ Mae Hadaka Jime, Rear Naked Choke/Hadaka Jime.