To explain, Johnny, I'm afraid, is probably an exercise in futility but I'm always up for a challenge once in awhile.
I think I shall begin with the obvious and go from there. Johnny is a less than well adjusted human being. He has the nasty habit of killing people. Usually quite brutally. It is very rare that the people he killed are not assholes. There have been a few exceptions like the perfectly nice guy he killed simply for his blood. Oh that's another thing, Johnny's house has a bit of a mind of it's own. But I'll get to that later. It also turns out that Johnny was chosen to soak up all the free floating bad vibes that roamed the earth. He was chosen for this job because he is so introverted, it wouldn't have affected him that much. Whoever made that decision didn't account for the fact that all those bad vibes can make a person go quite insane, as in the case of Johnny. Okay, so the badness wasn't the only cause of his insanity, he was already pretty insane, but being a "flusher" didn't help him any.
Another piece of obvious information: Johnny is not a nice guy. He kills people for being mean to him. I mean the really little things like talking during his favorite movie, insulting him about his appearance, or using a word he doesn't particularly like. He's taken a flying leap over the line of over-reacting. But that's the thing though, you're not supposed to like him. You're supposed to recognize the facts that life is not fair and people are petty and obnoxious (with a few rare exceptions).
He lives in a shack with a many leveled basement filled with torture devices and interesting toys of impending doom. He uses them to destroy evil people who, he thinks, deserve it. Like I said, they usually make fun of him because of the way he looks and for that, they automatically suck, but they don't deserve to die, it's just another example of Johnny taking things a little too far over the line of over-reacting. He uses the blood of the people to paint a wall in one of the rooms. Behind the wall is an unnamed evil (by the way, it's not a moose). He uses the blood to keep the wall wet and the thing trapped. Eventually the thing gets out, kills a few people and ... it's a really long story. Go buy the comics, you silly thing, you.
He has a few companions: his next door neighbor, Todd (aka Squee) and Nail Bunny, a pet rabbit he had that he fed once and promptly nailed to the wall. Nail Bunny is Johnny's voice of reason it's a little strange to explain so go out and get the books yourself. There are the doughboys, Psycho Doughboy and Mr. Eff. They are Johnny's other voices but after awhile they become, self-aware, and one of them actually encourages Johnny to end his miserable life. This leads to some strange and interesting stuff.
Niaha's Disclaimer: If parts of this explanation page made no sense at all, it is most likely due to the fact that it was not created in one stream of conciousness and was cut and pasted from bits and pieces of something I had already written plus a few added bits.