The present progressive (or continuous) is a compound construction of two verbal forms that cannot be separated by any other word: the auxiliary verb + the gerund. The progressive may be used in different tenses by changing the conjugation of the verb estar (past, present or future) and leaving the gerund in its intact form.  For now let’s focus on the present progressive:

Subject Pronoun + estar (conjugated) + gerund

bajar = to go down

What’s a gerund? In English, gerunds all end in -ing: reading, dancing, singing, etc. (For more on gerunds in English, see the entry on gerunds in the Guide to Writing.)

In Spanish, the ending of the gerund depends on the kind of verb:

• for -ar verbs: drop the “-ar” and add → -ando
• for -er and -ir verbs: drop the “-er” or “-ir” and add → -iendo
• Stem-changing -ir verbs (not -ar or -er verbs!) change their stem vowels as follows: o-u, e-i. Note: verbs that change from e-ie and e-i in the present tense both change e-i in the gerund form.
• The gerund of the verb ir is irregular: yendo.

sigan = keep, continue (plural imperative of “seguir”); subir = to go up

Ejemplos:

• -ar verb:
  • Tomar → tomando (taking)
  • Cantar → cantando (singing)
  • Comenzar → comenzando (starting) ¡OJO! Though this has a stem-change in the present it’s an -ar verb so its gerund is regular.
• -er verbs:
  • Beber → bebiendo (drinking)
  • Volver → volviendo (returning)
  • ¡OJO! Though “volver” has a stem-change in the present, it’s an -er verb so its gerund is regular.
• -ir verb:
  • Escribir → escribiendo (writing)
• stem-changing -ir verbs:
  • Dormir → durmiendo (sleeping)
  • Preferir → prefiriendo (preferring)
  • Servir → sirviendo (serving)

Note: To form a negative sentence in the present progressive, place the no in front of the form of estar: 

• No estoy escribiendo (I am not writing).

Remember that the present progressive is used to express an action in progress at the moment of expression. Note the differences in meaning:

• Estudio español. (I study Spanish/I am studying Spanish. a general description of the situation over a period of time: you are taking Spanish as part of your studies this semester.)
• Estoy estudiando español. (I am studying Spanish. an action in progress right now: you have your book out or a site open and you are actively studying a lesson or preparing right now.)

Note also: Although in English, the present progressive tense can refer to events in the future (“We are going to the movies tonight”), in Spanish the present progressive always refers to ongoing action. For future actions, Spanish uses the present tense or the future tenses.

• Vamos al cine este fin de semana. (We’re going to the movies this weekend.)