1. The main form of the verb is called the infinitive
The main form of the verb is called the infinitive. The infinitive consists of two parts: the ending and the stem. The ending is the last two letters. There are only three different endings: -ar, -er, and -ir. The stem is everything else, except the ending.
hablar: ending = ar, stem = habl comer: ending = er, stem = com vivir: ending = ir, stem = viv
With regular verbs, the stem stays the same, and the ending changes as they are conjugated.

2. Spanish Stem-Changing Verbs
With some verbs, the stem also changes when you conjugate them. In the present tense, there are three groups of stem-changing verbs:
o:ue e:ie e:i

3. How do these verbs work? Examples Empezar= e→ie Poder= o→ue
In one group of stem-changing verbs, the letter e in the stem changes to ie in all but the nosotros form. This particular type of stem-changing verb is found in all three verb types.
cerrar yo cierro tú cierras él, ella, Ud. cierra nosotros/as cerramos ellos, ellas, Uds. Cierran
Examples
Empezar= e→ie
Poder= o→ue
Pedir= e →i

4. Los verbos que cambian e→ie
Tener
Querer
Pensar
Empezar
Comenzar
Perder
To have
To want
To think
To begin (start)
To lose

5. Empezar
First, let’s just add all the correct endings.

6. Verb endings
If a verb ends in –ar, you add: o as a
amos an

7. Verb endings If a verb ends in –er, you add: o es e emos en
if a verb ends in –ir, you add: o es e
imos en

8. So, since “empezar” ends in “ar” (empezar), which endings will we add?
The “ar” endings: o as a
amos an

9. Empezar
empez o
amos as a an

10. Now, let’s add our stem change.
Remember, only the e in the stem can change.
Empezar
querer
If there are two e’s in the stem, the second one always changes.
preferir
empezar

11. Now let’s change the stems.
Remember, e can change to ie and the nosotros form never changes!

12. Empezar o
amos
empiez
empez as a an

13. Pedir e i o
pid
pedimos es e en

14. The o→ue verbs work the same way.
Poder
Dormir
Soñar
Volver
Devolver
to be able to (can)
to sleep
to dream
to return (to a place)
to return (a thing)

15. First, find the o in the stem that is going to change
Poder
Dormir
Soñar
Volver
Devolver

16. Then, decide which verb endings you will use.
For poder: o es e
emos en

17. Poder
p__d
pod ue o
emos ue es ue ue e en