A Spanish girl asked this same question yesterday. Take a look at this: http://www.italki.com/question/273667 Basically, they are different prepositions with different meanings and uses. The main thing to remember is this - it is impossible to translate a preposition (to, for, at, in etc) directly from Spanish to English, or from English to Spanish. Or any other language. So what should you do? The key is to learn complete phrases in English, not single words. If you remember simple phrases such as 'Let's go to the beach', you'll soon learn which prepositions are used in which situations. Good luck.