Is it digital? No, it's a film camera.
Is it good for someone trying to learn photography at a professional level?
-Well, as a starter camera, it's okay, but the cost of film gets expensive, the cost of developing even more, and you don't get instant feedback like with digital. It is definitely not a professional level camera!
Is it worth it for a used camera at a cost of $150?
-Definitely NO! You can get better cameras, used, for under $100.
Will it be able to store photos on a memory stick?
-No. It's a film camera. Only a digital camera (and only Sony digitals) can use a memory stick.
What should you get if you want a used digital SLR cheap?
-Look for a used Canon Digital Rebel, also called the EOS 300D. Expect to spend around $300 to $350 for a used one with lens. For a new camera with lens, try a Pentax K100D, for about $460 or so.