What if I don't see a token in metamask?

I'm curious, what should I do if I don't see a token I've purchased or acquired in my MetaMask wallet? Is it a common occurrence? Should I panic? Or are there specific steps I can take to troubleshoot this issue? I've heard of people adding custom tokens to their MetaMask, but I'm not entirely sure how to do that or if that's the right approach. Could you walk me through a step-by-step process to resolve this, ensuring that I don't miss any critical details? Any help would be greatly appreciated.