In English, 'advice' is what we call a mass noun. We can't say a(n) or use a number with these words; we need to add another word to do that: a piece of advice, a piece of information, two cups of flour, three glasses of water, and so on.
Nouns that we can* count, like cow, book, apple are (unsurprisingly) called count nouns, and we can say two cows, a (or one) book, etc. You need to add a count noun to a mass noun to use the mass noun with a or a number. A pound of meat, two pages of information, etc.
Hope that's helpful.