两:1.Used before a classfier or 半,千,万,亿,etc. eg,两公里(two kilometres);两岁的女孩(two-year-old girl);每隔两天(every two days);两个半小时(two and a half hours);两万元(twenty thousand yuan);2.both(sides);either(side) eg,两侧(both sides;either flank)小路两旁(either side of the walk);敌对的两军(contending armies);3.a couple;a few;some:再等两天(wait for a few (or a couple)more days);你再拿两个走吧(Take some more with you) 2: 2楼(second floor);这事我略知一二(I know a little about it);二者必居其一;其它的道路是没有的(Either one or the other,there is no other choice);二者不可兼得(You can't eat your cake and have it too);不二价(fixed price;no bargaining);三心二意(of two minds;shilly-shally)

i think when you do some arithmetic your should say 2,but when you talk something don't need arithmetic ,you shuld SAY 两，by the way ,when we say somebody or something 2,that mearns it must be carzy.

even though "二 and 两" means 2 (two), in Chinese context almost different. because : 2=1+1; 两=1;1. let me take a very simple example: you + your lover are 2people ,in Chinese,we say :两人;两个人，couse you are you,your lover is your lover;induvidual but when you both do something together,IN Chinese ,we say 二人,例如:二人世界(you+your love spend time together)二人转...

For example: two people means 两个人 two dollars means 二块钱 二两 equals 100g two pieces -- 两块 / 两片 the second - 第二 twenty - 二十

as far as my concerned, you should use 两 while you are wanna express quantity，for example: 两个人(means two people),两种产品 (means two kind of products)。 of course, have another difference, i can send you material for you study.