Without the word sein (to be) we simply wouldn't exist. Out of all the verbs (or doing-words), it is the most important one.
So, let's introduce you to sein
I am
ich bin
you are
du bist
he/she/it is
er/sie/es ist
we are
wir sind
you (plural) are
ihr seid
they/you (formal) are
sie/Sie sind
Notice:
1. There is almost no resemblance between sein and it's conjugated forms! We call verbs that don't follow the pattern of conjugation, irregular verbs.
2. The good news is, sein is so frequent that you will learn it very quickly.
3. Second good news is, there is not other verb as irregular as sein.
The rest of the verbs will be irregular just in the forms of du and er/sie/es, the others will always be super regular and predictable! So it is still worth it to learn those endings!