There are many things in college you can do that you couldn't/can't in high school
College offers a variety of courses and activities that high school does not
There are many things in college you can do that you couldn't/can't in high school=大学では高校では出来なかった・出来ない事がたくさんある
College offers a variety of courses and activities that high school does not=大学は高校にはなかった様々な授業や活動が提供されている
offer=提供
variety=色んな種類の
course(s)=授業
activity(ies)=活動
Good luck!
There are countless things that you can do in college/university that you can't do in high school.
There are countless things that you can do in college/university that you can't do in high school.
大学では高校ではできないことがたくさんできます。
上記のように英語で表現することができます。
countless は「無数の」「たくさんの」という意味の英語表現です。
お役に立てれば嬉しいです。
またいつでも質問してください。