I am so happy I have discovered this forum! I bought my first fish yesterday and I realize I don't know everything I should!!! I am happy there is a group of people that are willing to share their experience and expertise - I will be needing them!
Welcome sunny, what size tank do you have? What kind of fish are you interested in?
Be sure to read all the articles and threads in the beginners section, especially those that tell about the nitrogen cycle. Pick up a master test kit, to test your ammonia, nitrite, and nitrate levels in your aquarium. It is possible with lots of TLC to cycle your tank with a fish, before you get any more you should wait till your tank has completed this cycle. It can take weeks, so be patient. I have found taking time to plan out your tank can be half the fun! Good Luck !