HEEL is where the dog walks on a loose leash (without pulling) next to your left side with his front legs in line with your knee. He must maintain that position no matter what speed you walk (slow, normal, fast) and while you turn at right angles both left, right and about turn. The dog must come to an automatic SIT position when you stop without being given any additional command to sit.
Competition obedience requires a lot of practice, patience, precision and dedication to teach if you want to enter your dog for shows in obedience. To start with you must get a set of rules that explain the exact details / positions etc. because without first understanding exactly what is required in an competition it is impossible to even begin training for competition.
To enter into an obedience competition in a dog show for the first title, you do not need to learn more than the five exercises I mentioned but if the dog fails to perform with only a single command for each exercise, and does not do so quickly and with precision, you will lose marks. Imagine that in obedience competition you start with full marks and they are deducted for every mistake you or the dog make and at the end if you still have the minimum total required for the title, a title will be awarded.