Этот means "this" and тот means "that", and both agree with the noun: этот, эта, это, эти. Это on its own also means "this is", with no noun after it. To ask a price, say сколько стоит? for one thing and сколько стоят? for several.
Examples
- Сколько стоит эта рубашка?
- How much is this shirt?
- Я возьму тот, не этот.
- I'll take that one, not this one.
- Сколько стоят эти туфли?
- How much are these shoes?
The mistake to avoid
Это книга means "this is a book"; эта книга means "this book" - one letter, two different sentences.
Where this fits in
Food & ordering, Russian A1: Order at a café or restaurant, ask for the bill, and talk about basic food and drink.