Automatic Writing
There are two kinds of automatic writing. The first kind, and the most popular when trying to find information on it, is the "spiritually possessed" kind. People believe (and I'm not saying it is or is not fact, simply that there is no proof for or against) that a spirit will use one's hand, poised with a writing utensil over something to write on, such as...well...paper, to write. Sometimes a message, sometimes a story, other times it's a letter or a poem or some scribbles that look more like asemic writing than anything real. People profess that they "have the urge" to write and then they start writing without really realising what's being written--because the spirit is the one actually writing.
The second kind of automatic writing is to write from the subconscious. Some people find this incredibly easy and others not so much. Some people say they don't realise what they've written until they've written it. As for me, well, I've never been able to achieve writing without some idea of what I'm writing. A word or a sentence or anything comes to my mind and I write it, but it must always come to my conscious first, and then I will write that down. The point is not to edit what you're writing, even if it doesn't make sense. With practice, I'm sure, I'll get better--as well as anyone who tries it.
If pictures come to mind--which are usually just scribbles of sorts or unconscious doodles, which a lot of people do quite often--then it's called "automatic drawing." It is quite the same, except not words, but drawings.
One may think asemic writing is automatic drawing, but I believe it lies somewhere in the middle. Asemic writing is something that looks like some kind of text or like it has some meaning in some language, though it does not really (not in the same way as writing words, anyway).
Automatic writing can be done on paper or using a computer or typewriter. One may post their writings on the internet or attempt to publish them in a book (lulu.com is great for self-publishing), or he or she may keep them private. Using this form of writing, one may look into their subconscious briefly, just as we do with our dreams.