Confirmation for prep + relative pronoun

I am grateful to you, CJ. I am aware of rewriting the same thing because in my first language, there is no similar structure, and therefore It is difficult to understand for me. In fact, my first language is considered an Agglutinative language, and there are huge logical differences from English. For example, all the relative clauses rules are equal to 2 letters at the end of the word without space.
Moreover, I am looking for different sources, such as English Grammer in Use series, Cambridge Dictionary, other grammar books and websites, and yes there is lots of information, but it is not clear for me, Maybe other people who have different native languag, or who is smarter ones than me can understand the logic easily.

Finally, I understand the logic, and I learned thanks to you. Again THANK YOU SO MUCH!

If you wonder about my first language, It is Turkish.