Well, fishkeeping is more than just reading instructions.
Hold off on any fish for two weeks at the LEAST, giving time for bacteria to colonize in your water, stabilizing your water parameters.
Speaking of water parameters- yes, Bus is right.
You will need to get your hands on a liquid test kit to test for pH, ammonia, nitrite & nitrate levels.
DO NOT buy Test Strips.
Yes, these ARE easier and faster, however they are inaccurate and could lead to a big mistake.
These are useless.
Make sure with any fish you purchase you search for there size, behavior, etc online before you get them, as many Pet Stores are limited in which fish will fit what tank.
Any more questions?
It's what FishForum is her for.