Most of the ab exercises workout your abs in some way, some are more efficient than others.
I listed the three best ab exercises to be done at home.
Special thing about these exercises is that you don't need any special equipment to do them, you can do them while watching TV at home.
Maybe an exercise mat is a good idea so that the hard floor under your back doesn't feel so bad.
First exercise is sit ups.
Yes the good old sit ups is still effective as it was ever.
If you feel it is too hard for beginning to do you can try basic crunch.
In the sit ups you basically lift your upper body of the ground while keeping your knees bent and feet on the floor.
Touch your knees with your elbows at the up position.
Second exercise is toe touchers.
Again lie on your back get your hands and feet up and try to touch your toes with your finger tips.
Do this exercise in controlled motion, so that you don't start rocking or get otherwise unbalanced.
This exercise is very much similar to basic crunch as how it makes your abs work, but more effective.
Third exercise is V-up.
Somewhat similar to toe touchers, but your starting position and how one repetition ends is different.
Start out by being as straight as possible on the ground while keeping hands directing upwards.
From there get your straight feet and hands up and touch your toes and return back to the initial position.
This exercise makes your abdominal muscles work all around since they need to stabilize your core also.
These are just three of the effective home ab exercises you can do.
There  plenty of others if you don't feel comfortable with these exercises.