Welcome to TFF, and this wonderful hobby.
In addition to the good advice from other members, something of a general nature that hasn't been mentioned yet concerns shoaling fish. All of the tetras, rasbora, danio and barbs are shoaling fish, which means they live in groups of hundreds and must have a group in an aquarium. Obviously the tank size can limit this. Some other fish are shoaling too, like cories, loaches, rainbowfish. Some species need more in the group than others might, but a good rule to remember is always have more and not fewer than any "minimum" as the fish will be healthier and better off.
Always research a species before buying it, and do not take the advice of staff in the fish store. Some stores may be better than others in this respect, but it is a wise practice to take down the name of a fish you might like and then check it out on this forum or Seriously Fish. This can save a lot of trouble and grief, and the poor fish.
Water parameters are essential to know; these you may be able to find on the website of your municipal water authority. GH is general or total hardness and the most important.
Byron.