Determiners are used in front of nouns to indicate whether you are referring to something specific or something of a particular type.
Determiners are different to pronouns in that a determiner is always followed by a noun. Therefore personal pronouns ( I , you , he , etc.) and possessive pronouns (mine, yours, his, etc.) cannot be determiners.
The definite and indefinite articles a/an/the are all determiners.
You use a specific determiner when people know exactly which thing(s) or person/people you are talking about.
The specific determiners are:
"The dog barked at the boy."
"These apples are rotten."
"Their bus was late."
You use general determiners to talk about people or things without saying exactly who or what they are.
The general determiners are:
"A man sat under an umbrella."
"Have you got any English books that I could have?"
"There is enough food to feed everyone."
Either and neither are used in sentences concerning a possible choice between two items.
Either can mean one or the other (of two) or each of two.
I've got tea and coffee, so you can have either. (One or the other)
The room has a door at either end. (Both)
Neither means not the first one and not the second one.
Neither of the students were listening.