You use “have” with verbs, and “had” with nouns. Here are some examples. The verbs/nouns are highlighted with brackets.
i.e. “have”
“I have {ran} an entire mile in 7 minutes before!”
“I have {held} a baby, but I was afraid to drop it so I gave it back.”
“I have {taken} my cat to the vet in the past.”
i.e. “had”
“I had a {bowl} of cereal for breakfast this morning.”
“I had a {dog} named Lollipop once.”
“She had a {nap} scheduled after school.”