Question

when a verb is iregular and when it is regular verb

Answer 1

In English, a regular verb doesn't change in past tense or participle tense, we only add -ed.
For example:
Work in past is Worked
Cook 》Cooked
Watch 》Watched

When a verb is irregular, it changes the word for another different, change something in the word or doesn't change anything. For example:

•Lie in past is Lay and in participle is Lain.
-In this case the word change for another.

•Give in past is Gave and in participle is Given. - In this case something change in the word.

•Cut in past is Cut and in participle doesn't change.


Espero te sirva.