Have is present tense whiles had is past passive voice of have. ( Past tense ) Meaning of have: possess, own, or hold. Had: past and past participle of have. [ Possess, own, or hold.]

Today, we have a Toyota. Ten years ago, we had a Ford. In our lives, at various times, we have had Toyotas, Fords, Hondas, Chevrolets, and Plymouths.

"Have" will be used far more often because "have had" indicates more particular meanings. Examples of "have" : 1) I have a lot of books (present tense) 2) I had a lot of books (past tense) These sentences and their meanings are pretty simple, and the most common way to use "have." "Have had" is most often to indicate something that has happened before that does not usually happen, or to indicate a change. Examples: 1) It is very unusual to see the same customer more than once per day, but I have had some of my regular customers come in up to three times in the same day before. 2) Today has been terrible, but I have had worse days in the past.

"Have" is a verb, indicating possession. We typically use "have" as a main verb with an object to talk about common actions. for example: have breakfast, have a shower, have a walk... "have had" is a combination of two verbs: present tense "have" and its present perfect object "had". "Have had" is present perfect. We use the present perfect tense when we want to connect the present with the (recent) past in some way and this will appear as "has had" or "have had" for example: I have had dinner. (I have eaten dinner) I have had a bath. (I have taken a bath) Have they had their breakfast yet? They've had a glass of orange juice, but they haven't had anything to eat yet.