1) Determiners specify nouns and include articles, demonstratives, possessives, quantifiers, and numbers.
2) The definite article "the" is used to refer to something specific or unique. The indefinite article "a"/"an" is used for non-specific references.
3) Demonstratives like "this" and "that" indicate whether something is near or far from the speaker.
4) Possessives like "my" and "your" show who or what something belongs to. Quantifiers indicate amounts.