Oh okay. Well, honestly, you can't decide what your life's calling is in a night, or even in a week or in months. You find out what you want your career to be through experience. I really recommend that you volunteer at a vet's office for a while to decide if you want to do that. And when you're in college, take computer classes and biology classes and decide which one you like better. I'm assuming that your stepdad has a career. He should know that he didn't wake up one morning and know what he was going to do with his life. He probably found out through experience.
You don't "pick out" what you want to do with your life. Most college freshmen are "undecided" in terms of their major for at least a year; sometimes until their Junior year. Basically, my advice to you is don't "pick out" a career. Go to college and decide what you enjoy most while you're there.