Learn Spanish (Spain): ¡Qué guay! Mañana vamos a la playa. - How cool! Tomorrow we're going to the beach.

In Spanish, when you want to exclaim "How [adjective]!" you always use Qué. You use Cómo to ask "how" something is done, but for exclamations describing a quality, it is always ¡Qué guay! or ¡Qué bonito!

Is guay a word I can use in any Spanish-speaking country?

Guay is very specific to Spain. It is a colloquial, everyday word meaning "cool" or "awesome." While you will hear it constantly in casual conversations in Spain, it isn't really used in Latin America, where people might say chévere, bacano, or genial instead.

Why does the sentence use the present tense vamos instead of the future tense iremos?

Just like in English, Spanish often uses the present tense to talk about planned or certain events in the near future. Saying Mañana vamos a la playa is extremely natural and actually more common in everyday speech than using the formal future tense.

Can I say mañana estamos yendo to mean "tomorrow we are going"?

No, and this is a common trap! In English, we use the continuous "-ing" form for future plans, but in Spanish, the present continuous (estamos yendo) is strictly for actions happening right at this exact second. For future plans, always stick to the simple present: vamos.