Hello Moeee,

e is the exponential function. Read boffin stuff here: http://en.wikipedia.org/wiki/Exponential_function

Most calculators have one, and it's usually labled "Exp". In excel you use the function exp(...). Basically, it's just a special number that has an infinite number of decimal places, but lucky for us the calculator has a good approximation!

So to do e^7, on the calculator you would do EXP -> 7.

And yes, Ln is Log to the base of e. Also known as the natural log.