Efficient and effective are adjectives.
We use efficient to describe something or someone that works in a quick and organised way:
The new online banking system offers a convenient and efficient way to check your account.
[extract from a reference for someone applying for a job]
I have always known James to be highly competent and efficient in all aspects of his job.
We use effective to describe something that gives you the results you want:
Taking this tablet is a very effective cure for travel sickness.
In this light, the camera is more effective if you use the flash.
