tiny little black spot on tooth

It's probably a cavity but as above, you should see a dentist to be sure. It's better to go sooner rather than later, as if it is just a small cavity it's very quick and cheap to get fixed. If you wait for a long time then whatever it may be it's likely to get worse and become more painful and require longer and more expensive treatments.
Cannot overstate how much better it is to get a cavity filled early than wait for it to need a root canal (and then a crown...).