help with drop down lists

[EvilTree]

HI, im new to this place
and i was wondering how to make a drop down list thingy

im trying to make a calculater but not for math but for other things

an example is here:http://www.geocities.com/ypppear/PEARcal.htm

i want to make something like that but with different words in the slots

what is the code???