Is it true that a good way to conclude your composition is to create a sentence that refers back to your opening point?
This is a technique that is taught by many, many English teachers and can be effective depending on the type of essay and the audience. A good rule of thumb to start with when determining whether it is effective or not is whether the teacher has asked for it or suggested it as a good way to conclude an essay. If they have, then it is absolutely a good way to conclude. If you cannot think of another good way to do it, this is also a way to try and be sure that the reader understands that you've reached the end and hopefully made a point about what you started with.
If you look at professional writing with a broader audience than just a teacher, you will see this sort of thing less frequently and when you do it is typically more subtle and definitely more artfully done. This isn't easy to pull off without pandering to the reader and making them feel like you are talking down to them but at times it is done beautifully and effectively.
It is also typically not a bad idea on a standardized test or timed writing assessment where you want to be very straight-forward and make sure that your organization is super clear since most scorers will only have a minute or less to spend with your composition.