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irregular verb
sein
('to be') which is irregular in English as 
well (I am, you are, he is....).
pronoun verb
in English:
ich
bin
I
am
du
bist
you
are
er/sie/es
ist
he/she/it
is
wir
sind
we
are
ihr
seid
you (plural) are

---

sie
sind
they
are
At least 1st and 3rd person plural are the same. Another important verb is 
haben
('to have'):
pronoun verb
in English:
ich
hab
e
I
have
du
ha
st
you
have
er/sie/es ha
t
he/she/it
has
wir
hab
en
we
have
ihr
hab
t
you (plural) have
sie
hab
en
they
have
You see, it's not too irregular—only the 2nd and 3rd person singular constitute a small exception since 
the 'b' has vanished. English is somewhat curious in this respect as well: 'I have', but 'he has'. Future 
lessons will introduce you to the many 
irregular
verbs in German. But you should now recognize what 
is happening to the verbs in German sentences. They are reflecting the person and number of their 
nominative case subjects. Recall these sentences from past lessons (verbs underlined here):
Danke, es geht mir gut
Thanks, it goes well with me (verb is 
gehen
)
Ich habe viel Arbeit
I have much work (verb is 
haben
)
Ist er zu Besuch?
Is he visiting? (verb is 
sein
)
Du bist ein Schwein!
You are a pig! (verb is 
sein
)
Wie heißen Sie?
What are you called? (verb is 
heißen
, and 
pronoun is formal)
Wir spielen eine Stunde lang!
We play for one hour! (verb is 
spielen
)
Sie liegt am Ausfluss des Zürichsees.
It lies at the outlet of Lake Zurich (verb 
is 
liegen
)