Irregular verbs are those that have their own forms II and III (the Past Simple and Past participle). If a verb is irregular it will have its II and III forms in brackets in dictionaries:
wear (wore, worn)
Regular words just add -ed in these forms: look (looked, looked). They are called regular, because they all change their forms according to the rule.
If you're dealing with a verb and you are not sure how to use it in, say, the Past Simple or Past Perfect, look up in a dictionary - if there are no other forms indicated - it's a regular verb.
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