The Spanish "future progressive" is formed using the formula below:

future of estar + present participle of the action verb = future progressive

The Spanish future progressive - el futuro progresivo - is very similar to its English counterpart (will be + -ing). In both languages, the future progressive expresses an action that will be in progress at a certain point in the future.

Si necesitas algo, estaré leyendo en el jardín.
If you need something, I'll be reading in the garden.

Mañana, estaremos caminando en Barcelona.
Tomorrow, we will be walking in Barcelona.

Estará trabajando cuando llegues.
He will be working when you arrive.

The future progressive is similar in usage to the future, but with an emphasis on the fact that the action will be in progress at the moment in question.