Regular verbs are verbs in which the present tense is changed by adding "d", "ed" or "ied".
Examples: Scream -- screamed / Cry -- cried / Die -- Died
Irregular verbs are verbs in which the present tense has the same spelling as the past tense.
Examples: Cut -- Cut / Hit -- Hit
Irregular verbs also refer to those verbs where the spelling of the present tense is different from the past tense (but not because of the addition of -d, -ed or -ied)
Examples: Make -- Made / Swim -- swam
I hope this helps.