Well, the first thing you're gonna need is a fish tank. Bigger ones are easy to care for, but then they are also more expensive, so work out how much you think you can afford.
Next will be a filter - you need to buy one that will is suitable for the size tank - if you buy from a shop, hopefully the staff there will guide you.
Since you are in Nigeria, I would have thought you wouldn't need a heater, but if your home is cooler inside than outside, then you will.
Next you need to consider the substrate - what goes on the floor of the tank. I have sand, others have stones. When you decide, buy it, and wash it big time. Put it in the bottom of the tank.
Then you want to think about decorations - real plants, fake plants, real wood, fake wood, other plastic ornaments. Buy them and put them in.
Water is next, make sure you buy a decent water conditioner product from the store, follow the instructions, put the water in the tank slowly so it doesn't disturb the substrate.
Then you need to do the single most important thing in fishkeeping. We call it cycling the filter, and it means to grow bacteria in your filter to deal with the waste produced by the fish. There are two ways of doing so. To read more (and all this stuff is available in more detail elsewhere on the site), go to the Cycling Your Filter section.
That's a VERY basic overview of preparing your tank, then you need to consider what fish you are having. Probably best if you do the preliminary stuff first, then we can talk about the fish.
You'll probably have loads of questions, it's best to ask them in the threa, rather than starting loads of different threads all over the place.