First of all, let's be clear. I know, without any trace of a doubt, that life is just life is just life. There is no ultimate purpose or meaning. But none of all that matters. Once you fully realize the nothingness of everything, you're left in a downward spiral of despair. Ain't nobody got time for that. Finding meaning in the meaningless is perfectly fine, as long as you first realize the truth. Downward spirals are themselves completely pointless, even in the less-than-grand scheme of our tiny human lives. What's the point of life, you ask? Why even try?
Well, why not? What is the point of not trying? You only have one life, so why spend it lonely and miserable? We should spend what little time we've been allowed doing the things we enjoy. In order to achieve happiness, one must tuck away that knowledge of meaninglessness and invent some fantastic reason for being. Why not be happy?

crime and punishment

The only "crime" Candide is guilty of is being completely innocent and impressionable. He really doesn't know anything in the beginning, but this is by no fault of his own. He is like a child who must be taught the ways of the world. When a child gets curious and starts hitting people, its parents scold it because hitting people is wrong. They might decide to show it this wrongness by scolding in terms the child can better understand, like revoking certain privileges like television and sweets. Eventually, the kid will begin to understand that what was done was wrong. Candide has obviously either been brought up in some other, less effective way, or is just too stupid to learn this way.
The first punishment, the one that sets off every other painful experience Candide has, was being kicked out of the castle for going after Cunegonde. This action was arguably not wrong at all, just the product of young love, but it was deemed inappropriate by the king. If Candide had any sense at all, he would have made an effort to keep his affair a secret, but we know this is not the case. The king doesn't really realize how dumb Candide is, and isn't really in the wrong for kicking him out because anybody else would have known better. Candide doesn't really deserve this punishment because something less harsh might have actually taught him better to at least be more discreet in his pursuits of Cunegonde. It's not his fault that nobody ever taught him the ways of the world, but anyone who is still so ignorant by the time they reach that age can't expect anything less than harsh punishment and repulsion from society.

knowing

How do I know what I know? The only thing I know for sure is that I don't know how I know what I know.

I know most things, common, everyday things, because I am told them by people with more experience in that area. There isn't any really reliable way to check if they actually know. I just take it on faith.

A better question would be: Do I know anything? If you have an idea, no matter how close to the truth it may be, you don't know it if you aren't positive that it is right.

There isn't some all-knowing presence with which to check our facts. So we can't ever be positive that anything is right, so we can't every really know anything. Who's to say that there isn't a real name for the color of the sky, one true thing to call it, something other than "blue"? We don't really know anything, we name things and speculate and use science until we are as close to the truth as we can ever hope to be. And yet that truth may be the complete opposite. Some people realize this and try to search for it, but this is certainly in vain. I don't know that it's in vain, but I assume it and accept it because it's all I can do.