probiotics-what are they

Hi, this is Bellski, I was just wndering if someone could explain probiotics to me.  I keep reading about them on here.  I have uc and want to know.  That are probiotics, how do I get them, should I take them, and is it a prescription?  Thanks, Bellski

Here are some helpful links:

http://articles.mercola.com/sites/articles/archive/2004/09/29/probiotics-benefits.aspx

http://www.medicinenet.com/probiotics/article.htm

http://www.jinipatelthompson.com/articles_by_jini.php#

(Scroll down to last article link)