Kesa Gatame is generally taught early on in grappling, as it is fairly simple to teach and execute.  To begin, tori and uki sit back to back.  Tori then leaves enough space and uki lies down.  On uki’s right side, tori grabs ukis right arm with his left arm, deep above the elbow.  Keep his arm tightly against your body.  Tori’s right arm grabs around uki’s neck and grabs the uki’s collar.  Right knee should be deep under uki’s shoulder.  Left leg should be bent back, almost in a hurdler’s stretch.  Bend head forward and bury it next to uki’s head.  You don’t want to allow uki to attempt to pull back tori’s head.  This would allow escape.  If uki tries to roll away from tori remove right hand from collar and post with hand.  If he rolls back in to you, resume mat hold.    Everything must be tightly executed, thereby immobilizing the uki.