Regular and irregular verbs

An English verb can be regular or irregular. Regular verbs form their past and past participle forms by adding –ed.
Examples are given below.

Walk – walked – walked
Dance – danced – danced
Paint – painted – painted
Work – worked – worked

Irregular verbs form their past and past participle forms in different ways.
There are mainly three types of irregular verbs.
Verbs in which all the three forms are the same (e.g. put – put – put)
Verbs in which two of the three forms are the same (e.g. sit – sat – sat)
Verbs in which all three forms are different (e.g. drink – drank – drunk)
Some verbs can be both regular and irregular. Examples are:

Burn – burnt – burnt (irregular)
Burn – burned – burned (regular)

Dream – dreamt – dreamt (irregular)
Dream – dreamed – dreamed (regular)

Lean – lent – lent (irregular)
Lean – leaned – leaned (regular)