I changed my settings in the preferences box to fullscreen, now I can only see my document window other than that it's just black. I'm not good with computers at all and I don't even know how to explain what the problem is. Basically it's impossible to get back to the dialog box that I marked in the first place to unmark it.

Please tell us what your operating system is, as well as your Inkscape version.

To fix your current problem, try just closing Inkscape and open it again. If it's still black, we'll see what we can do to help.

Meanwhile, I'm not even sure there's a fullscreen setting in Inkscape Preferences. I just did a quick look and didn't see any such....and I can't think of anything that you might have interpretted as such. Hopefully restarting Inkscape will fix the problem, but if it doesn't, tell us what you see. If you know how to make a screen shot, please upload it into your reply as an attachment (below the Submit button, Upload attachment tab, and follow prompts).

If you don't know how to make a screen shot, no worries, we'll get through it
-- Is it just the canvas (the area that you draw in) that's black?
-- Do you see the menus on the menu bar?
-- Do you see any icons?
-- Do you see any scroll bars?

That will be enough to start

Confused! wrote:I changed my settings in the preferences box to fullscreen, now I can only see my document window other than that it's just black.

If by chance you are using Mac OS X and changed the preferences of X11/Xquartz to use Full-screen mode, these steps will restore normal behavior:

1. (launch X11/Xquartz if it isn't already running)
2. use Cmd+Option+A to leave X11 full-screen mode
3. open the X11 preferences and untick '[x] Full-screen mode'