There are two main types of nouns: count nouns and non-count nouns. Count nouns refer to things that can be counted individually, like planets or sandwiches, while non-count nouns refer to things that cannot be counted individually, like rice or advice. Non-count nouns often have no plural form and are used with words like "some" rather than "a" or "an". However, some non-count nouns can become countable by adding a phrase that gives them a form or container, such as "a piece of furniture" or "a cup of water".