What exactly is the concept of jen in Confucianism?

I know Jen kind of means kindliness, but I don't know the concept really, and I can't find it on the Internet. Could you please explain to me more of what Jen is and what the concept is??? Thanks =]
Oh, and could you tell me which of the concepts of Confucianism is most important (like Jen, Li, etc.)? Thanks again =]
And please explain that concept.

That is Forest Gump's girlfriend

Confucianism?Jen (pronounced Rena), humaneness or human-heartiness.

34 While Li emphasizes restraint by external rules, Jen deals with human nature, or the inner person. The Confucian concept, especially as expressed by Confucius? principal disciple, Mencius, is that human nature is basically good. Thus, the solution to all social ills lies in self-cultivation, and that starts with education and knowledge

The term, Rena, is unquestionably rough to translate; it could be summed up to mean "complete virtue", as it embodied the values of a number of moral obligations that Chinese Society followed during the time of Confucius and onward.(Do-Dinh 102) The character for Rena is composed of two graphic elements, one representing a human being and the other representing the number two. Based on this, one often hears that Rena means "how two people should treat one another." While such folk etymologies are common in discussions of Chinese characters, they often are as misleading as they are entertaining. In the case of Rena - usually translated as "benevolence" or "humaneness" - the graphic elements of a human being and the number two really are instructive, so much so that Peter Boodberg suggested an evocative translation of Rena as "co-humanity."