There are three types of verbs based on their last vowel in the dictionary form: a-verbs, e-verbs, and и-verbs, i.e. those ending in a, e, and и, respectively, in the form found in the dictionary. For verbs that end in -и in the dictionary, in order to form the present tense, the final -и is replaced in the first person singular with an -a- and removed completely in the third person plural. Then the endings you are already familiar with are added:
јас -(replace final -и with -a)м
тие -(remove final -и)ат
where the - represents the dictionary form.
Note: with verbs ending in -oи in the third person singular form of the present tense, a -j- is added between the -o- and -a- in the first person singular and third person plural. To see this in action, view the I-verbs part 2 tutorial.