The problem with any type of guide, like the one Barb linked, is that it is very general to the point of being of minimal use. For example, it says Tetra are compatible with Tetra, but many are not compatible with many other tetra.
Compatibility involves several factors. Filtration (some fish need more water movement, others need little if any), decor (some fish need caves, bogwood, rock for hiding spots), plants, the length or height of the tank (active swimmers need more length), water parameters, temperature. Then we get to behaviours, for which many species are individual.
Once you know the tap water parameters, this will narrow down a bit. But then you have to decide what type of tank do you want? Do you want quiet, sedate fish? Or more active fish? These do not work well together. An aquarium of truly "compatible" fish, in all senses of the word, will be more enjoyable for you because the fish will be healthier.