There are some people who say that in English it is wrong to end a sentence with a preposition, but others disagree. Most people do it in everyday speech. Often when the preposition comes at the end of a sentence, it's because the preposition was part of another phrase that was rearranged. Example: Here is a statement: "I did it for love." If you rearrange this sentence to make a question, you could have: "What did you do it for?" The question is based around the pattern "do it for," so the preposition "for" comes at the end. A more elegant-sounding way to ask the question is: "Why did you do it?" You could answer that question with "I did it for love," and it would make sense. Let's try another example: Q: "Where did you come from?" A: "I came from Peru." The question is based around the pattern "come from," so you can end the question with the preposition "from." It can be the same with statements. Example: 1: "Do I have to go to school?" 2: "Yes, you have to." The pattern "have to" is the focal point. Saying "you have to" is a short way of saying "you have to go to school." Because the verb phrase "go to school" came right before it, we understand what the person has to do. Let's imagine that Person 1 responds to Person 2: 1: "But I don't want to!" The pattern "want to" is now the focal point. Because we know the verb phrase is "go to school," we understand that the meaning is "I don't want to go to school." Sometimes if the preposition is part of an idiom, it can come at the end of a sentence too. Examples: "The cars are passing by." "This is behavior I will not put up with." "I'm going to sit this one out." "The bookcase fell over." I hope this helps!

It is the grammar rules for forming a questions. I am going to the store. Where are you going to? I am going with Alice. Who are you going with? 'For' can be a little tricky. I am doing this to get ready. What are you doing this for? Notice that in this last example, 'for' doesn't occur in the statement form of the sentence. This is just how the language developed.