It means that you can see something, it seems to you that you can take it, it is close to you but in fact you can't. For example you can see cherries on the tree but you can take it because you do not have a ladder to teaк them off .

That means that you can't get certain thing, though it seems that you can do it easily. Literally "an eye sees, but a tooth does not reach"

You can see it but can not get it.

"So near, and yet so far" is the best short version. (https://translate.academic.ru/%D0%92%D0%B8%D0%B4%D0%B8%D1%82+%D0%BE%D0%BA%D0%BE,+%D0%B4%D0%B0+%D0%B7%D1%83%D0%B1+%D0%BD%D0%B5%D0%B9%D0%BC%D0%B5%D1%82/ru/en/)