Die Wörter это und вот

Two tiny words do a lot of work in your first Russian sentences: э́то ("this is, that is, it's") and вот ("here is, there is", the word you say while pointing or handing something over).

это does not change

In "this is + noun", э́то stays the same whatever follows: Э́то стол, Э́то ла́мпа, Э́то окно́, Э́то мои́ друзья́. It does not agree in gender or number, much like French c'est.

Do not mix it up with э́тот / э́та / э́то / э́ти, "this" in front of a noun, which does agree: э́тот стол (this table), э́та ла́мпа (this lamp). Compare:

• Э́то кни́га. This is a book. (a full sentence)
• Э́та кни́га интере́сная. This book is interesting. (э́та agrees with кни́га)

Questions and negation

• Что э́то? What is this? Кто э́то? Who is this? Russian uses кто for people and also for animals: Кто э́то? - Э́то наш кот Ба́рсик.
• Э́то не чай, э́то квас. This isn't tea, it's kvass. The не goes before the word it denies.

вот in everyday use

Вот is what a waiter says putting down your borscht (Вот ваш борщ), and what you say handing over your passport (Вот, пожа́луйста). It points; it does not describe. "This is a museum" in a guidebook sense is Э́то музе́й, not Вот музе́й.