You sure do jump in with both feet, huh?
Have you run /usr/X11R6/bin/xf86config yet. That will set up your config file for x. Here's a link to the how to.
That link is the printable version. That should get you started. Make sure you have all the info on your hardware when you do the config. It asks a lot of questions. Keyboard, monitor resolution, video card and such.
If you have made it this far you should be OK. You have came a long ways. Gentoo is really nice.