1) What does the bible say about purgatory?
Nothing **specifically**. There are some passages (in both Roman Catholic and Protestant Bibles) that support the concept of something similar to Roman Catholic Purgatory - but (again) nothing *specific*, nothing that *indisputably* refers to Purgatory or a state identical to Purgatory.
2) What does Christianity or Catholicism say about purgatory?
Basically, Purgatory is a Roman Catholic doctrine. The doctrine teaches that humans must be "purged" of their sinfulness before entering sinless Heaven, and this "purging" occurs in a place called "Purgatory". Note that the "processes" believed to occur in Purgatory include both forgiveness of certain types of sin (not all types) and a more general purging of a sinful nature. Here is the official Roman Catholic teaching (it's not very long, starts at 1030):
http://www.vatican.va/archive/ccc_css/archive/catechism/p123a12.htm#1029
3) I'm a good person but has done alot of "sin".
Then you - like all of us - are not a "good person". You are a sinner in need of forgiveness - like all of us.
4) Now correct me if I'm wrong, but isn't purgatory the punishments you receive before being sent to heaven?
The Roman Catholic concept of Purgatory is an unpleasant "place", one where the time spent by a person roughly corresponds to their sinfulness. However: I don't think that it is typically viewed as **punishment**. You see from the official description that people there experience a (symbolically) "cleansing fire" - not a "punishing fire". Obviously "fire" sounds quite unpleasant/painful - but (again) it does not seem intended as any sort of **punishment**. The wicked are punished for their sin, the saved are NOT punished for their sin because they are *forgiven* of their sin, but the Roman Catholic Purgatory purging process seems painful despite **not** being punishment.