Hallow Ammar! Welcome to the Forum. Have, has and had are auxiliary verbs used with pefect and perfct continous(progessive) tenses as helping verb. They can be also used independently to show possession. Such as: I have a bike. They had two houses 5 years ago. If you have any specfic problem in understanding their uses you can ask as separate thread.
In English, we generally use 12 tense forms of a verb, which is the critical element of the predicate of a sentence. A verb indicates the timeof an action, event or condition by changing itsform and tense. A verb has four forms and three tenses. The four forms are (i) Infinite or basic or dictionary form (ii) past (iii) present participle or “ing” form and (iv) past participle. Depending on the time frame each verb has three tenses. They are (i) present (ii) past and (iv) future.These are basic tenses and each basic tense has four tense forms which are used to describe different timing of an action. These are (i) simple (ii) progressive (iii) perfect and (iv) perfect progressive. Here examples of 12 tense forms are given using the verb – “Write” Simple Progressive Perfect Perfect progressive Present I write. I am writing I have written I have been writing Past I wrote I was writing I had written I had been writing Future I will write I will be writing I will have written I will have been writing