I appreciate your effort to explain , thank you very much .

Use "have" with I, you, we, they (I/you/we/they have got a cat) Use "has" with he, she (He/she has got a cat) "had" is the second form of "have/has", use it when you talk in the past time. (I/you/we/they/he/she had got a cat in 1998) Also, we use have/has when we use Present Perfect time (I/you/we/they have never been to France or He/she has never been to Italy) and there's a phrase "I/you/we/they have to (do smth)". It means that you need to do something VERY much. For example: "I have to improve my English". We use "can" when we talk about possibilities. For example "I can do this", "you can do this". Any pronoun+can+activity. That's not all, but I think it would be better to look for explanations in the Internet, 'cause it will take much time to explain.