I am a young graduate seeking for employment. How do I answer to "what are your achievements" since I have no prior experience?

Tell them about everything else you've excelled at - sports, hobbies, etc - tell them about your interests and how far you've taken it - tell them about you're passion and what you HOPE to achieve in the future!

Tell them... your... achievements?

Either that, or start getting some experience. Anything will do...

I wouldn't dig down as far as saying things like "I volunteered at a homeless shelter in high school"

Interviewers can smell a bs-er from a mile away.

Talk about extra curricular stuff in school.

An interview is a selling job, you are selling yourself. So you want to present the advantages of "buying" you.

Don't forget your academic achievements, you are a graduate after all.