We use ¿cuánto?, ¿cuánta?, ¿cuántos?, and ¿cuántas? to ask how much of something or how many.

¿Cuánto cuesta el libro?
   How much does the book cost?

¿Cuánta deuda tiene usted?
   How much debt do you have?

¿Cuántos jugadores hay en un equipo de fútbol?
   How many players are there in a soccer team?

¿Cuántas almohadas usa para dormir?
   How many pillows do you use to sleep?

To talk about how much of something, we can use adjectives of quantity. Such adjectives tell how much or how many: mucho (a lot; many) and poco (a little, few).

Tenga mucho cuidado.
   Be very careful.

Ella tiene muchas uvas.
   She has many grapes.

Tienen muy poco interés.
   They have very little interest.

Este carro usa muy poca gasolina.
   This car uses very little gasoline.

If these words describe a noun, they must agree in gender and number. Adjectives of quantity almost always come before the noun.

“So much” and “as much”

tanto [never *tan mucho!].
Note also that the plural form “so many” is tantos/as.

Por favor, no bebas tanto.
Please, don't drink so much.

Ella trabajó tanto como yo.
She worked as much as I (did).

Nunca he visto tantas personas en un mismo lugar.
I've never seen so many people in one place.

Expressing “Most of”

“Most of” is usually expressed as la mayor parte de

Dormimos la mayor parte del día.
We sleep most of the day.

Pasamos la mayor parte del día en el centro comercial.
We spent most of the day at the shopping center.