Hello :)
ЧЬЯ/ЧЕЙ/ЧЬЁ/ЧЬИ are interrogative pronouns, in English they mean "WHOSE."
The interrogative pronoun ЧЕЙ agrees in gender, number and case with the noun or pronoun it refers to. For example:
Чья это собака? Whose dog is this? (feminine)
Чей это кот? Whose cat is this? (masculine)
Чьё это письмо? Whose letter is this? (neuter)
Чьи это очки? Whose glasses are these? (plural)
Used in interrogative sentences, i.e. one asks questions using them.
"ЭТОТ" (neuter is "ЭТО") translates as "THIS"; it's a Russian demonstrative pronoun. Demonstrative pronouns are commonly used when you are pointing to something, or indicating what you are talking about with your body.
You may have noted that "ЭТО" can be both a demonstrative pronoun and a demonstrative adjective of the neuter gender. So, "это яблоко" may mean both "this apple" and "this is an apple", and without context you can only tell them apart by the first capital letter and a full stop in case it is a sentence.
It's good to remember that the neuter singular form "ЭТО" is used as the introductory word in Russian sentences: "Это собака" ("This is a dog); "Это мальчик" (This is a boy); "Это девочка" (This is a girl); "Это пальто" "This is a coat"; "Это кошки" ("These are cats").
In cases "Это авто -- твоё" (This is your car") and "Это -- твоё авто" (This car is yours) "ТВОЁ" is a possessive pronoun ("your", "yours" familiar singular); it shows to whom a subject mentioned belongs to; it must agree in gender, number and case with the thing possessed.
I hope, this will help.
Best regards