Where can I sell my core?

Excuse me, I'm a bit new to the cryptocurrency market and I'm wondering where I can sell my core holdings. I've heard about various exchanges and platforms, but I'm not sure which one would be the most suitable for my needs. Could you please recommend a reliable and secure platform where I can liquidate my core investments? Additionally, I'm also interested in understanding the process and any potential fees or taxes involved in selling my cryptocurrency. Could you provide a brief overview of the steps I should follow and any potential pitfalls I should avoid? Thank you for your help in navigating this market.