Abs form part of the CORE (foundation of your body). The most important part of any work out is CORE.
The CORE is the area beginning at the pelvis and it extends to the rib cage. It is the foundation of the body and is vital in the holding of posture. Most lower back pain and injury is caused by poor CORE strength. Anyone starting out should start with isometric exercise, as this is an exercise that you do not move the joint throughout. It comprises you to hold the exercise in one position, usually against gravity, which acts as the resistance.