Why is the iguena classified in the animalla kingdom?

Do you mean Iguana?

There are only 3 kingdoms, animals, fingi or plants, did you think it was a plant or like a mushroom?

(OK, some consider there are 5 kingdoms or more now but the others are for the truly tiny stuff like bacteria and protozoa).

Seriously, think about your question.

An iguana has eyes, ears, teeth, genitals, legs,claws, a tongue. Is it likely to fit any other category than animal?

Animal is everything that is not fungus or plant.

Animal kingdom is next divided into chordata - with back bones - and without.

It has a backbone.

It is a reptile - like a lizard, snake, gekko, ......

Does it have leaves or roots,? No.

Does it have to be planted in soil.? No.

Does it grow like a parasite on another living thing? No.

Then it can't be a fungus or a plant.