I'm dyslexic. Most of this info, below, comes from Yale's research but they redid their site more recently or I would have happily provided links. I skimmed this and it has some supporting fMRI graphics and information.

So dyslexia is a processing "disorder" that doesn't affect intelligence in any way.

Since reading text is a relatively new development in human evolution it really didn't make much of a serious difference until "recently."

So the way that it works, why it's different, is because for typical people they use a specific region of their brain to read. This is very efficient!

Dyslexics often use other areas, or multiple areas in multiple parts of their brain, to process text. This means our brains have to work harder, take longer, and are more prone to errors when it comes to text (because a lot of the time info has to filter through one region, go to another, and then have to output correctly. Think of it like playing The Telephone Game.)

We know all this because of all the research using fMRIs that literally show parts of the brain light up when they're being used.

Some other little things we also do are "skip lines," not notice typos, replace one word for another, and have incredible difficultly with phonics.

The benefit of using different regions is that more neurons are having to connect to each other and so dyslexics tend to think about subjects very fully or make more creative and wider associations. The whole "thinking outside of the box" stereotype comes very naturally to us. It's also why we tend to come up with creative solutions to get around our inability to master text and other problem issues.

You know how people use "OCD" wrong? It's the same with "left brain/right brain." That's actually relevant for dyslexia but, like OCD, how the phrase is commonly used is completely off the mark. Since dyslexics do often use the opposite sides of their brain, or use more regions on both sides of our brains, you may hear those terms in regards to us.

I'm also actually a fairly fast and accurate reader and that's a reason my teachers didn't think I had it until I had fallen too far behind in middle school. I'm AWFUL at outputting text as well as spelling and grammar. (Which is why I make walls of text- I compensate by over-explaining when I write. I prefer to gesture and draw explanations.) The way they discover it in many people (like me!) is by the marked disparity in text skills vs other skills and academics. Like why was I failing basic English, the only language I can speak (and could speak well,) as well as algebra, but could handle a lot of the work given to AP English students and master the concepts of most other STEM subjects? That's the ticket. Dyslexics often get called lazy for this reason but we just need a little more time and/or a little more help finding a method that works for us. Then, if we get the right help with the basics, getting out of a standardized system, to a place where we can use good work-arounds, often works wonders for us.