Adverbs of quantity (demasiado, bastante)

Demasiado

To express that something is excessive, use demasiado (too / too much). When describing an adjective or how much an action is done, it acts as an adverb and never changes form.

The hall is too small for the party.
El salón es demasiado pequeño para la fiesta.
They eat too much and there are only three cakes.
Ellos comen demasiado y solamente hay tres pasteles.

Bastante and Suficiente

Bastante can mean "quite" when describing an adjective, or "enough" when describing an amount of something. You can also use suficiente to mean "enough".

The table is quite big and we have enough food.
La mesa es bastante grande y tenemos suficiente comida.

When these words describe plural nouns rather than verbs or adjectives, they act as adjectives and must match the noun in number (for example, adding an -s to become suficientes).

There are enough chairs for the guests.
Hay suficientes sillas para los invitados.

Poco and Solamente

To talk about small amounts or set limits, use poco (little) and solamente (only).

The guest drinks very little.
El invitado bebe muy poco.
We only need enough ice, not too much.
Solamente necesitamos suficiente hielo, no demasiado.