You also need either a lot of live plants or a bottle of ammonia solution.
Fish excrete ammonia, which is poisonous to fish. You need something in the tank to remove this ammonia, and there are two ways of doing this. The first is to use live plants, and more than just the odd one or two. Plants use ammonia as fertiliser and if there are enough of them they will use all the ammonia made by the fish. With this method, the tank is planted, then you wait a week or two to make sure the plants are growing and not dying. Then add fish a few at a time, monitoring ammonia and nitrite levels between additions, and only adding more fish if the readings remain at zero for a week. If they don't remain at zero, water changes must be done to get the readings down to zero.
However, if you don't want to have to look after plants as well as fish, you need to grow some bacteria to 'eat' the ammonia. This takes several weeks. The method for doing this fishless cycle is here
http://www.fishforums.net/threads/cycling-your-new-fresh-water-tank-read-this-first.421488/
If you just leave the tank running for a week with no live plants (or only one or two) and then get fish you will find yourself doing a fish-in cycle which involves testing the water every day and doing a water change every time you get a reading for ammonia or nitrite. Depending on the number of fish you put in the tank, it could mean several water changes a day. Using this method it can take a few months before the tank is fully stocked as you should start with only a few fish, then once the tank is cycled for those fish, add more a few at a time.
You also need to look on your water company's website for your tap water hardness. You need both the number and the unit, and ignore any words they use. Fish need to be chosen from those that originate in water with hardness close to your tap water.
Since you are new to the hobby, I need to warn you not to believe anything a fish shop says. Most of them don't know or don't care and will say any rubbish to make a sale. Members on here are not trying to sell you anything and will give you better advice.