Ask HN: Advice for an 18yo looking to do an internship?

I'm looking to do an internship or work experience before I start University mid-feb next year. I'll be studying engineering, but I also really enjoy the software development (both embedded and web) I've done competing in robotics competitions over the years.

How should I go about asking companies about internships? Especially since I haven't even finished highschool yet. Are there things (portfolio, CV, etc.) that I need to prepare before I start asking around?

I'm located in Australia if that helps.

Thanks in advance.