Best High-Yield Savings for a 18 year old?

I currently only have $1000 saved up, but by end of summer I plan on having $2500, and I will put my refund check from school into here too. I need to be able to transfer money as needed because of costs for school (like books).

I bank with a credit union (they do not offer High-Yield Savings, only CD), and I have a credit card with AMEX (Blue Cash Everyday) and Discover (Student Card).

I want to open a high-yield savings account but my parents do not know what that is, and I do not know where the best place to go is. Any advice?