Henna!!

 I've decided that im long overdue for exploring this rave called henna. I need to do some research on it but me being lazy me,im stalling for now. (its ok i dont want to try it until im after im one year natural anyway) if anyone already knows the answers to my questions, please be a dear and save me the hassle of looking for them.

• what exactly is henna?
• what does it do?
• is there a certain time of the year it should be applied? (ex winter? for extra moisture)
• how often should one henna?
• what was YOUR experience like with henna?
• I've heard there are types of henna...how true is this?

Those are my questions for now....thanks in advanced for any that you decide to answer.. *smiles*

LOve,