Since you are introduced to pronouns, it's time to learn your first verb. It is going to be 'to be' and 'not to be': būti, nebūti.

Būti:

aš esu (I am)
tu esi (you are)
jis, ji, jie, jos yra (he, she, they are)
mes esame (we are)
jūs esate (you are)

Nebūti:

aš nesu (I am not)
tu nesi (you are not)
jis, ji, jie, jos nėra (he, she, they are not)
mes nesame (we are not)
jūs nesate (you are not)

As you notice, all verbs end in ti in their infinitive form. Remember this ending. In informal situations, however, it is often shortened to t (būt, nebūt).