New fish died...what could be wrong?

I bought 2 fish yesterday, and now theyre both dead. What did i do wrong? i just placed them in a fish bowl.. is there a certain procedure in setting up a fish bowl before you add your fish? What are they? and by the way, i found really tiny fish-like organisms in my fish's body!! it was really tiny had to use a magnifying gl to see it clearly... it was moving, even when my fishies were already dead.... what are theyy...?