a/an + [countable noun]
[countable noun]-s
some/much + [uncountable noun]
a glass of / a piece of + [uncountable noun]
A countable noun is a thing you can count: one apple, two apples. An uncountable noun is a thing you can't count one by one, like water, rice or music. It has no a or an, and no plural.
Use a or an for one, and -s for more than one. One countable thing always needs a word before it: a, the, my, this.
An uncountable noun takes a singular verb (is, was) and words like some, much or a lot of, never a number.
Common ones: water, milk, coffee, rice, bread, money, music, time, work, homework, information, advice, furniture, luggage, news, weather.
To count them, put a container or an amount in front: a glass of water, two cups of coffee, a loaf of bread, a piece of advice.
Some nouns are both. Coffee is the drink, and a coffee is one cup of it. Chicken is the meat, and a chicken is the animal.
Information, advice, news, furniture, luggage and homework are uncountable, even when you mean many things.