what is the difference between 'son' and 'están'?
'son' and 'están' are the conjugations of the verbs 'ser' and 'estar' respectively in the plural (formal) second person and plural third person form. Hence, a more precise question would be what is the difference between 'ser' and 'estar'?
The quick answer is 'ser' is used when referring to permanent or long lasting properties, while 'estar' is used for temporary states or locations. I found a very good explanation along with mnemonic aids to help remember the difference, and would suggest looking it up (i hope its ok to post external links here):
By the way, if it sounds too complicated, don't worry. It just takes practice, then you won't even need to think which one to use where :)