에 this one is used when designating a word with a location. usually used before verb or noun this is like ; at, on, in, etc....and sometimes 'of' (으)로 this one is used when you are designating a word for a use of something. usually used before verb like ; with hammer망치로 , with nail 못으로 but you cannot use it exatcly like "with" because 망치로 못 doesnt make sence. 로 can be used after words that has no bottom additions like 가기구게고보아바다아나 으로 is used after words that has the bottom things like 못국박막참 but some exceptions are there ah... i wish i could explain it better.