We say "I have a car." We do not say "I has a car."
Unluckily in our books of grammar and courses on english the use of HAS, HAVE with pronouns is not made clear. Most of the poeple have a concept of using "HAS" with singular subjects except "I" and "HAVE" with plural subjects which is wrong and people just cram it. The use of HAS and HAVE with different pronouns does not base on singular plural technique.
Actually the use of HAS, HAVE with different pronouns must be taught on the basis of persons instead of numbers. Students should be taught that HAS is used when subject of the sentence is third person singular i.e (He, she, it, singular names) and HAVE will be used if subject of the sentence is 1st person, 2nd person or 3rd person plural i.e (I, we, they, you, plural names).
There are three persons in every language and so has English.
The third person includes pronouns like he, she, it, one and all singular nouns anything i.e inanimate things, people, concepts, animal etc. This 'S' added to the third person singular of simple present in used only in English. It is not used in French, German, Italian or other languages and it is actually called 'The third person singular S'. It does not change the number or make a noun plural like from boy to boys..