An Overview of the Present Progressive:

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.

Verbs ending in -ar, e.g.: tomar

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, e.g.: comer, vivir

Verbs ending in -er or -ir add -iendo to the stem, e.g.: estás comiendo, están viviendo

• when an -ir or -er verb stem ends in a vowel, e.g.: leer, traer, creer, oír, the 3rd person endings change i to y e.g.: él creyó la historia, ellas leyeron el libro
  

-ir verbs with a stem change in the present, e.g.: yo pido, ellos duermen

-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