Determiners help identify things and show quantity, including articles like "a" and "the", possessives like "my" and "your", and demonstratives like "this" and "that". There are two main groups of determiners: Group A determiners identify things, while Group B determiners are mostly quantifiers like "some", "any", "each", and "enough". Certain Group B determiners can only be used with singular or plural nouns, and some can be used with both countable and uncountable nouns. Multiple determiners can be used together depending on the group and whether the combination makes sense.