Effective means that something works: it is successful. Efficient means that something doesn't waste any time or materials. Examples: Cleaning the floor with a toothbrush is effective but not at all efficient. Preparing some questions for a language exchange ahead of time makes the meeting both more effective and efficient.

Efficient means doing things in a right way while effective means doing the right things. Example: Situtation: You are an employee given the task to shop for the supplies needed at work. Effective → You buy the things you need and also did some window shopping sincw you're already there. Yes, you achieved your goal but you wasted time Efficient → you buy the things you need and went straightly back to your office. You wasted nothing :) Thank you! Hope this'll help you :)