The present progressive in Spanish is used to describe an action that is unfolding or in progress at the moment of speech. It is formed by combining the present tense of estar, conjugated with the appropriate subject, followed by the present participle form of the verb, e.g.: estoy hablando.
The form of the present participle depends on the infinitive form of the verb. Verbs ending in -ar add -ando to the stem:
Verbs ending in -er or -ir add -iendo to the stem, e.g.: estás comiendo, están viviendo
-ar and -er verbs with stem changes in the present do NOT have stem changes in the present progressive, e.g.: están jugando, estás perdiendo.
-ir verbs (only -ir verbs) with stem changes in the present e.g.: decir, dormir, preferir, retain their change in the present progressive for all subjects, e.g.: estamos pidiendo la comida