Congrats on the new setup. There are all kinds of water conditioners on the market you can buy. Any local pet store will have it as well. Seachem Prime is one of the best and works the fastest with credit to DAVIDFBT's post.
I would also buy a test kit for your tank. Or if you dont feel comfortable doing this you can take a sample of your water to a pet store and they will be able to test it for you. Although having one on hand is recommended for times you cant get to a store. They are extremely easy to use and have great directions. I always recommend the dropper kit and not the strips.
When your tank has cycled for a while with all the accessories in it (Plants, rocks, etc), you can start adding starter fish. Dont buy the fish you want right away. Put a few smaller fish like zebras or rosies in first. The reason for this is when you add fish to the tank it drives up your ammonia levels which is toxic to fish. The smaller and hardier fish can tolerate this more than your more exotic fish. So after the ammonia spikes from the waste your tank will start forming bacteria that kills off the ammonia. This bacteria is known is Nitrates which is also toxic at high levels. The Nitrate is then converted to Nitrite. So as the Nitrates and Nitrites go up the Ammonia goes down. After the ammonia is at zero the nitrates and nitrites will then fall to normal levels. This is the time you can add the fish you want because you now have a biological filter. This process usually takes a couple weeks but in smaller tanks like yours, I would say a 7-10 days would be sufficient.
Now that your tank is established, I would test the water and then I would slowly add in your fish. I say slowly because every fish you add is going to cause the ammonia levels to rise again. One fish every week is safe, testing frequently. You may know this already, but I will say it anyway. When you get the fish from the store they will be in bags. You dont want to just dump the fish into your tank as this can cause shock. you will want to place the bag in the water for about twenty minutes to balance the difference in temerature, and then dump them out. Another good thing to do is add a little aquarium salt to your water. This reduces stress and even helps prevent and treat some of the more common fish diseases Some people dont do this so its optional. Fish are more prone to disease when they are stressed so it helps when introducing them to a new tank.
After you have your new fish in, its just a matter of doing maintenance. The first couple weeks after you stock the tank, I would test the water every day just to make sure your levels dont jump around decreasing it to every other day. Make sure you do a small water change every couple of weeks (for a lightly stocked tank), about 25% of the water. Add your water conditioner and salt to the tank before adding the new water. Also make sure the new water temp isnt more than a couple degrees more or less than the tank water. So....lol. Sorry about the novel. Here is a summary.
1. Setup tank with accessories and fill with water.
2. Add water conditioner and salt (optional).
3. Turn filter and heater on.
4. Cycle for a couple days and ensure temperature is within range.
5. Add starter fish.
6. Cycle with fish for 7-10 days.
7. Test water. Make sure ammonia is zero and nitrates/nitrites are minimal.
8. Slowly add new fish.
9. Maintain and enjoy.
I hope this helps out. Your at the right place if you have anymore questions. Kudos for taking the time to research and ask for advice before taking it on. Not enough people do it, and blow it. Good luck.
