Irregular verbs are verbs that are not conjugated (or changed) in the normal way.
Normally verbs in the past have an -ED on the end. e.g. want - wanted, like - liked.
Irregular words are ones that DON'T have the typical -ED ending. e.g. go - went.
They change completely.
But irregular verbs are not only with the past tense. Sometimes in the present and many times in the Past Participle.
In the present tense, verbs normally have an S on the end for the third person (he, she, it)
I speak, she speaks; They live, he lives. But some verbs don't follow these rules:
e.g. I have, you have BUT he has, she has.