In the case of -ir stem changing verbs the stem vowel changes. For example:
Verbs with stems that end in a vowel also have an irregular form:
The verb estar must be conjugated to match the subject pronoun. For example:
I am eating.
You are singing.
He is speaking.
She is drinking.
We are speaking.
They are studying.
Just like English, Spanish uses the present progressive tense to describe actions that are occurring while one is speaking (e.g. John is writing a letter). Also similar to English, the present tense is used to describe actions that one does repeatedly or habitually (e.g. John writes a letter every morning). One difference between the two languages, however, is that in Spanish the present tense can also be used to describe progressive actions. For example:
¿Qué haces? / ¿Qué estás haciendo?
What are you doing?
¿Qué escuchas/ ¿Qué estás escuchando?
What are you listening to?
Progressive tenses: estar + gerund.
To form a progressive tense, use the appropriate tense of the verb estar immediately in front of the gerund, e.g.:
No me molestes; estoy trabajando.
Don't bother me; I'm working.
Estábamos almorzando cuando llegaron.
We were eating lunch when they arrived.
Estuvimos haciendo ejercicio por tres horas.
We were exercising three hours [Or: We spent three hours exercising.]
Dudo que estén practicando a esta hora.
I doubt they're practicing at this hour.
Note that any tense can be used to form a progressive, even the preterit as given in the third example above [note that there the action is viewed as having been limited to a three hour period]. However, the present and imperfect tenses the ones most frequently seen.
Caution: As the name indicates, the progressive tenses express an action viewed as being in progress. Do not use the progressive for other purposes, such as for expressing a future action: “We're leaving for Mexico tomorrow” (Salimos para México mañana [NOT Estamos saliendo).
The Present Participle or Gerund
Gerundio ó Progresivo Gerund Present Participle Present Progressive