Have has to do with possession, and to have something is to be in possession of it.
Has is the third person singular present tense of 'have'. This just means that it is used when you are speaking in the third person singular, i. e. , with the pronouns he, she, and it.
'Has' is the third person singular present tense. 'Have' is the first and second person singular present and plural tenses and the third person plural present tense. 'Had' is the past tense for both 'has' and 'have'.
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