The gerund, or past participle, functions alone or with another verb to form the progressive tense.
To make the present participle, the -ar, -er and -ir endings are dropped from the verb infinitive forms. To the stem of-ar verbs add -ando, and to the stem of -er and -ir verbs add -iendo. An exception occurs in words like leer, creer, oír, ir, and construir. The present participle of this kind of verb avoids an unaccented i between two vowels and becomes y. Thus:
tomar: tom- + ando –> tomandoperder: perd- + iendo –> perdiendo
abrir: abr- + iendo –> abriendo
creer: cre- + yendo –> creyendo
oír: o- + yendo –> oyendo
ir:- + yendo –> yendo
In addition, stem-changing verbs present another complication in the formation of the present participle. Note in the table how the stem changes as the verb transforms to the present participle.
preferir (ie, i) prefir- + iendo –> prefiriendopedir (i, i) pid- + iendo –> pidiendo
dormir (ue, u) durm- + iendo –> durmiendo
There are a number of ways that the present participle can be used independently, but by far the most common occurrence is to translate the English word by plus a verb ending in -ing, such as "By studying one learns a lot" or "By playing dice one can lose a lot."
In English one often states that "I am going...," a declaration that is usually rendered in the simple present indicative. If, however, the emphasis of the speaker is to convey an action in progress the progressive may be used.
The present participle is used in conjunction with another verb,
usually estar, andar, seguir, venir, ir, or some other verb
of motion, to convey an unfolding, progressive action.