In order to study and remember the different conjugations of the Praesens Activum well, it is important to take a close look to the differences between the five conjugations.

FOURTH CONJUGATION

The basic vowel in the fourth conjugation is i, the endings are -o, -s, -t, -mus, -tis and -nt (-re for the infinitive). Be careful: in the first singular form the basic vowel doesn't disappear following the presence of the ending o, which does happen in the first conjugation. Pay also attention to the third person plural: there u is added as a binding vowel. The example verb is audire (=to hear, to listen), the stem of that verb is aud.

Verbum audire - verb to hear, to listen (stem = aud)
audio - I hear
audis - you (s.) hear
audit - he/she/it hears
audimus - we hear
auditis - you (pl.) hear
audiunt - they hear

Some other verbs of the fourth conjugation:
nescire - nescio - to don't know
scire - scio - to know
sentire - sentio - to feel
venire - venio - to come