Uneven lies attempts to duplicate the real life effect of the golf ball being above or below your feet or on an uphill or downhill lie. It's a great feature that adds massively to the difficulty of the game but has been critised for being too severe.
The way it works is if the ball is above your feet when you play it it will go to the left, the opposite is true when it's below your feet. When the ball lies on an uphill slope the club used automatically has more loft, therefore the ball flies higher but not as far as normal. The reverse is true for a downhill lie.
This mimics real life but as said, is slightly over the top at times although it has been improved since it's release.
You can judge how severe the lie is by looking at the box surrounding your lie indicator. A black box means flat ground, no effect on the shot. Green is slight to moderate slope and orange is pretty damn steep. I honestly don't know if there's a red box but if there is your ball is probably resting on a cliff.
There are also dots moving along the 2 axis of the box to give you a good idea of the severity of the slope, pretty much like the dots showing break when putting.
I hope this is the sort of info you're looking for.
It takes a bit of getting used to but can be very addictive. I started playing the uneven lies tour organised by Corwyn and love it.