Irregular verbs are an important feature of English. We use irregular verbs a lot when speaking, less when writing. Of course, the most famous English verb of all, the verb "to be", is irregular.
What is the difference between regular verbs and irregular verbs?
One good way to learn irregular verbs is to try sorting them into groups, as above.
If in doubt, a good dictionary can tell you if a verb is regular or irregular.
Here is a list of irregular verbs in English.