XP Bar, Experience Points And Rest

The purple / blue horizontal line towards the bottom of the screen is the XP (experience bar). When it's full, you have achieved a new level and the bar will reset to zero. Each level requires more XP points to complete. If you mouse over the bar, it will flash up your progress in numbers, i.e. x/y, e.g. 15000/33800.

The purple bar is the normal bar. An explanation pop up when you mouse over the bar. A blue bar is a well resting bar. You will gain double xp points than you would with a purple bar when the bar is blue. The bar turns blue after spending time in areas, such as an inn or a city where your level bar reads 'zzz'. It's therefore advisable to log out if you can in side an inn or city to accumulate more time in the blue bar status.

A notch will appear to indicate how rested you are. You will accumulate one bar of rest for every 8 hours spent in a resting area. The counter continues even when you're logged off. A maximum of 30 bars, i.e. 10 days of being logged off can be accumulated at any one time.

If you are outside of an inn or city, being logged off still accumulates rest points but at a rate of 25% of that gained whilst in an inn or city.

Do note that only combat points is affected by a rested state. Any xp points gained in any other way, such as quests or discovery / exploration, is not affected.

One last note: resting is based on character not account. By having more than one character you can continuously play in the blue state, earning double xp points and hence leveling up faster.

The official word on resting can be found here: http://www.worldofwarcraft.com/info/basics/resting.html