Trouble with my first time rigging for a college class.

https://imgur.com/a/mPlHX

I used the Edit Membership Tool (as instructed by the tutorial I'm following, given by my professor) to select all the points for each joint (eg. pic 1).
When I rotate joint 1 I get a weird deformation of the torso (pic 2). When rotating joint 2 (this joint is the parent for the whole skeleton) the whole body rotates. I need to get it to bend.
Any advice would be greatly appreciated.