El Presente

In the present tense we have three groups of regular verbs (that have the same stem for each different person and the following endings): 
Person
Infinitive ending in -ar
Infinitive ending in -er
Infinitive ending in -ir
hablar
comer
vivir
yo
habl o
com o
viv o
habl as
com es
viv es
él, ella, Ud.
habl a
com e
viv e
nosotros/ as
habl amos
com emos
viv imos
vosotros/ as
habl áis
com éis
viv ís
ellos, ellas, Uds.
habl an
com en
viv en
You can see that the verbs ending in -er and -ir are only different en the first and second person plural.
 
We have also verbs called stem changing verbs (that have exactly the same endings as the regular verbs but a different stem vowel from the infinitive in all the persons, except for the first and second person plural):
Change from e to ie
 
The following verbs have the same stem change: comenzar, empezar, negar, defender, encender, entender, perder, mentir, preferir
 
Change from e to i
pedir
pido
pides
pide
pedimos
pedís
piden
 
The following verbs have the same stem change: conseguir, impedir, seguir, elegir, repetir, servir
 
Change from o to ue
Person
Infinitive ending in -ar
Infinitive ending in -er
Infinitive ending in -ir
contar
volver
dormir
yo
cuento
vuelvo
duermo
cuent as
vuelv es
duerm es
él, ella, Ud.
cuent a
vuelv e
duerm e
nosotros/ as
contamos
volvemos
dormimos
vosotros/ as
cont áis
volvéis
dormís
ellos, ellas, Uds.
cuent an
vuelv en
duerm en
 
The following verbs have the same stem change: costar, encontrar, mostrar, probar, recordar, devolver, llover, mover, poder, morir
 
Change from u to ue
jugar
juego
juegas
juega
jugamos
jugái s
juegan
Change from i to í
enviar
envío
envías
envía
enviamos
enviáis
enví an
 
The following verbs have the same stem change: confiar, criar, guiar
 
Change from u to ú
continuar
continúo
continúas
continúa
continuamos
continuáis
continúan
 
The following verbs have the same stem change: acentuar, actuar, graduar, reunir
 
Change from i to y (unstressed i between two vowels is changed to y):
construir
construyo
construyes
construye
construimos
construís
construyen
 
The following verbs have the same stem change: concluir, distribuir, contribuir, huir, destruir, incluir

 Due to the general rules of pronounciation, some verbs have orthographic changes in the first person singular:
 
Person
Change from g to j
Change from gu to g
Change from c to z
coger
distinguir
vencer
yo
cojo
distingo
venzo
coges
distingues
vences
él, ella, Ud.
coge
distingue
vence
nosotros/ as
cogemos
distinguimos
vencemos
vosotros/ as
cogéis
distingís
vencéis
ellos, ellas, Uds.
cojen
distinguen
vencen
 
g - j:  Other verbs are escoger, proteger, elegir, exigir, fingir, corregir, dirigir
gu -g: Other verbs are seguir, conseguir
c - zc Other verbs are pareceragradecer, aparecer,
c - z: Other verbs are convencer, torcer, ejercer, mecer

Other verbs have irregular first person forms:


conocer - conozco (Similar verbs are: parecer, agradecer, aparecer, merecer, obedecer, ofrecer, permanecer, reconocer, conducir, introducir, producir, traducir

caer - caigo (Similar verb: traer)

hacer - hago

poner - pongo

salir - salgo (Similar verb: valer)

saber -


  Finally there is a number of so called irregular verbs, with more than one kind of spelling change. Some of them are:

decir - digo, dices, dice, decimos, dicen

tener - tengo, tienes, tiene, tenemos, tienen

venir - vengo, vienes, viene, venimos, vienen

dar - doy, das, da, damos, dan

estar - estoy, estás, está, estamos, están

haber - he, has ha (hay), hemos, han

ir - voy, vas, va, vamos, van

oír - oigo, oyes, oye, oímos, oyen

ser - soy, eres, es, somos, son

ver - veo, ves, ve, vemos, ven