how do i know if my stepfather likes me?

I guess he bought you things out of niceness to either you or your mom (she might have felt obliged to spend her money on those things if he had not).

He is right, he has no real obligation to you, except whatever the law says.

To judge whether he likes you, focus less on what he buys, and more on his other actions and body language.

Also, the better you treat him, the more he will come to like you over time. So be very good to him. This will make your mom happier when she sees you doing that.

Start your relationship with him by being friendly and sociable.

To help that, start learning interpersonal communication skills. You will benefit from these when you are with friends, at school, at work... all the time.

There are lots of self-help books about improving your interpersonal communication. Search "conversation", "interpersonal communication", "etiquette", and related subjects in your nearby libraries' catalogs. Or see what you can find at a book store. You could Google those topics, but you'll find that books are better written and more thorough than websites.

Read as many of those books as possible; each one will have different examples you will learn things from. Each contains the author's hard-won knowledge, the result of years of effort and sometimes suffering. Why learn the hard way what these authors have learned already? Why not just read the books?

Search for "How to Win Friends and Influence People" at the library. This book was written by Dale Carnegie; I recommend it and his other books even though they are old.

There is another book that comes very highly recommended by librarians, educators, and others (including myself). It is called "Changing Bodies, Changing Lives", written by Ruth Bell. It is partly a sex education book but it also talks about relationships and other things. Part of the book's genius is that it includes many quotes from teenagers, whom the teenaged reader is more inclined to listen to and consider relevant (instead of having only adults lecture and dictate to the teen reader).