To discuss the weather, you will need to use a form of the verb hacer - to make, do (full conjugation)

Let's look at some examples:

Hace calor. - It's hot (warm).

Hace fresco. - It's cool

Hace frío. - It's cold

Hace sol. - It's sunny.

Hace viento. - It's windy.

Now let's look at actual some typical conversations about the weather :

Desde anoche. Hace mucho calor. - Since last night. It is so hot.

En verano hace calor. - In the summer it's hot.

No me gusta el invierno. - I don't like the winter.

No me gusta la estación de las lluvias. - I don't like the wet season.

El cielo está oscuro hoy. - The sky is dark today.

Porque el clima es mejor allá. - Because the weather is nicer there.