Integrative core exercises (planks, hovers, mountain climbers, etc.) maximally engage core muscles and provide functional training. The core consists of all the muscles on the front and back of you body from shoulders to hips, muscles which must work together to transfer energy from lower to upper body and to stabilize. Integrated exercises promote stabilization by strengthening groups of muscles that must work together to stabilize the spine and create efficient movement. Integrative core exercises require a base level of muscle strength and coordination to be performed correctly. Technique is critical for integrative core exercises.
Isolated exercises focus on one group of abdominal muscles (crunches, reverse crunches, etc.). These are also very valuable and can be used to build the muscle strength required for integrative exercises.
It is a good idea to have a fitness professional help assess your level of strength, help you choose exercises appropriate to fitness levels and goals and help you find perfect form.