What are the different between regular and irregular verbs in past? 

Regular Verbs

Those verbs that form their past participle with ‘d’ or ‘ed’ are regular verbs. These verbs do not undergo substantial changes while changing forms between tenses.

1. If the verb ends with a vowel, only ‘d’ is added. For example:

PRESENT TENSE	PAST TENSE
Share	Shared
Scare	Scared
Dare	Dared

2. If the verb ends with a consonant, ‘ed’ is added. For example:

PRESENT TENSE	PAST TENSE
Want	Wanted
Shout	Shouted

Irregular Verbs

Those verbs that undergo substantial changes when changing forms between tenses are irregular verbs. The changed forms of these verbs are often unrecognisably different from the originals. For example:

PRESENT TENSE	PAST TENSE
Go	Went
Run	Ran