Progressive tenses are compound tenses that express actions viewed as being in progress. In English, this tense would be constructed in the following way, the auxiliary verb being "to be".
|TO BE |
|present tense ||I am||+||running.|
|past tense||I was||+||running.|
|future tense ||I will be||+||running.|
The construction of the Spanish progressive tenses follows the same structure. It's the conjugated auxiliary verb ("estar" = to be) + the gerund.
|present tense ||Estoy||+||corriendo.|
|imperfect tense (past) ||Estaba||+||corriendo.|
Like with English, the progressive tenses in Spanish can be created with any tense (present, past, future, etc.); however, it is most frequently formed with the present and imperfect tenses.
The gerund in Spanish, like in English, gives the progressive tenses their progressive nature. In the English sentence "I am running", running is the gerund; gerunds in English are essentially any words ending in "-ing". Spanish gerunds also have a common ending: "-ndo". Here are a few examples in both English and Spanish.
|English gerund (-ing)||Spanish gerund (-ndo)|
To form the gerund in Spanish, you remove the infinitive endings (-ar, -er, -ir) and add -ando to the stem of the -ar words and -iendo to the stem of for the -er and -ir verbs. For example: