How do I sell Altcoins for cash?

Could you please elaborate on the process of converting Altcoins into cash? I'm a bit new to the cryptocurrency market and would appreciate a step-by-step guide. Firstly, which platforms or exchanges should I consider for this transaction? Secondly, what are the necessary steps to ensure a smooth and secure transaction? Are there any specific fees or taxes I should be aware of? Lastly, how long does the entire process typically take? Your insights would be invaluable in helping me navigate this process.