1Z0-859 is upgrade exam. So, if you don't have any prior version of web component developer certification, you cannot appear to this exam.
Apart from that, 1Z0-858 is for JEE 5 and 1Z0-899 is for JEE 6. Personally, I would give certification for latest version possible.
What is your exact confusion? You can check out certification objectives on Oracle's website.
I hope this helps.
thanks 4 guidance. I wanted to know that if i go for 1Z0-858, will it be ok? and you said that we must have prior version of wcd certification for 1Z0-859. So i can't directly go for 1Z0-859, i am having SCJP certificate, will it be sufficient for it?