How do I cash in my foreign currency?

Hello there, I'm curious about the process of cashing in my foreign currency. Could you please elaborate on the steps I need to take to convert my foreign currency into my local currency? Are there any specific documents or fees that I need to be aware of? Additionally, are there any online platforms or services that you recommend for this purpose? I'd appreciate any guidance you can provide on this matter. Thank you in advance for your assistance.