When I got the board, I had no idea what to do with it. None. There didn’t seem to be a guide that I could find with google for people with my level of utter inexperience, so I thought I’d try to write one up.
First things first, you need some gadgets. Well, to get started the only thing you really need is a USB->Serial adapter. I don’t know much about these gadgets but was recommended this one and it works fine for me. While you’re in the shop, you’ll probably want to buy a handful of microSD cards. The faster and bigger the better probably, but 2 gigs or bigger is fine for playing around. You’ll need some way of writing to these cards as well, of course.
The xM comes with a microSD card that contains “The Ångström Distribution”. I don’t know what this is really, but it’s good to test that the board works, so pop the card in the slot in the board and plug the board in (I agonized for ages about this — I didn’t want to just plug it in in case a brief power contact would damage the board or something, but it seems to be the thing to do). Then connect up the USB/serial adapter and run “screen /dev/ttyUSB0 115200″. If the board has booted fully, you should get to a tty login. Type ‘root’ as the user name and you’re in! This default install is fairly plain — it’s a fairly minimal linux using busybox. But if it boots, the board likely at least somewhat works.
Next up is installing a Linaro daily build on the board and getting networking working so that you can install all the fun software that makes up Ubuntu!
If anything in this post strikes you as wrong or unclear, please let me know in the comments.