Hi! I’ve got articles for that. Keep in mind that no fish can be kept in tanks under 5 gallons and there are only two fish species I’d consider for a 5 gal. 5 gallons and up you’ve got a few more options but stock VERY carefully.
Skip the fish entirely if you’re a beginner or don’t have time to keep a super close eye on your tank. Might I recommend dwarf crayfish as a cool invertebrate alternative?