The words effective and efficient both mean "capable of producing a result," but there is an important difference. Effective means "producing a result that is wanted". Efficient means "capable of producing desired results without wasting materials, time, or energy".
The difference is that when something is effective it produces a result even if it takes some unnecessary resources to do so. When something is efficient, not only does it produce a result, but it does so in a quick or simple way using as little material, time, effort, or energy as possible. The following example sentences show how the two words are used.
The word effective puts more attention on the actual ability to produce a desired result. The word efficient puts more attention on the lack of waste in producing that result.
I hope this helps.