The Aorist describes, similar to the Imperfect, a past tense but the Aorist is used more often.
It is built different for the three conjugations:

Aorist 1st conjugation:

• Rule 1: There are differences in the 3^rd person singular, whose ending can be «-i» or «-u», depending on the preceding vowel.
  After «a, e, i, y», the ending in the 3^rd person singular is «-u», otherwise «-i».
• Rule 2: There are differences in the persons of the plural. Verbs ending in «-o» or «-e» in the singular change this vowel to «-ua» or «-ye».

In this verb, the 3rd person singular ends in «-i» because the vowel «o» comes after the stem. (see rule number 1)

«jetoj» is a verb whose vowel at the end of the stem is an «o». Therefore, in the plural, this verb changes this vowel to «ua». (see rule number 2)

Aorist 2nd conjugation:

The main characteristic of the verbs in this group is that the consonant «v» is not inserted between the stem and the ending.
The endings are somewhat different in the plural, but in the singular they are mostly identical to those of the 1st conjugation.

In the following table we compiled some of the most common verbs of the second conjugation and how the Aorist is formed:

Aorist 3rd Conjugation:
For the third conjugation, no scheme can be found so it is best to learn the forms as you learn the verbs.