Learn Italian: La camera è calda: accendo l'aria condizionata. - The room is hot: I turn on the air conditioning.

In Italian, objects and places (like la camera) use essere + caldo to say they are physically hot. You only use the verb avere to express heat (avere caldo, literally "to have heat") when talking about people or animals feeling hot.

Does camera mean a camera for taking photos?

No, camera is a "false friend" that means "room" (often specifically a bedroom, short for camera da letto). If you want to talk about a camera for taking pictures, you would say una macchina fotografica.

What is the infinitive of accendo and what is its opposite?

The infinitive is accendere, which means "to turn on" or "to light" (used for electronic devices, lights, or fires). Its opposite, "to turn off", is spegnere.

Since we are learning about formal imperatives, how would I formally tell someone to "turn it on" replacing the air conditioning with a pronoun?

Because aria condizionata is feminine, you replace it with the pronoun la. For the formal imperative (giving a command to a Lei), the pronoun must go before the verb. The formal command form for accendere is accenda, so you would say: La accenda!