Okay
Before you add any fish, you will need to cycle the aquarium. Once a tank is cycled a culture of beneficial bacteria will convert fish waste which is ammonia the bacteria will consume this ammonia (which is highly poisonous) and excrete it as nitrite, a less toxic type of ammonia. A new bacteria colony will form and it will convert nitrites into nitrates, the least toxic form of fish waste.
How to cycle an aquarium?
First add your heater and filter into the tank. Then add dechlorinated water. Switch on your gear. Now there are various ways of cycling. Fish less, getting seeded material and with fish.
I do not recommend cycling with fish. The ammonia eats at their gills and they will die a painful unecessary death.
Fish less cycling. The idea here is to use bottled ammonia to feed the bacteria with. A quick google search will give you plenty of idea, takes about 6 weeks.
Using seeded material. Using seeded material from another tropical cycled healthy tank will help to kick start your aquarium. Again quick google search. Takes under 1 week.
When cycling you will want to test your ammonia, nitrites and nitrates on a regular basis.
After your tank is cycled then you can talk about live stock.
HTH