Learn Spanish (Latin America): Usa la pinza para tocar ese carbón ardiente. - Use the tongs to touch that burning coal.

Not at all! In Spanish, tools that have two identical parts joined together (like tongs, tweezers, pliers, or scissors) can often be singular (la pinza) or plural (las pinzas) to refer to a single item. Both are perfectly natural and interchangeable in Latin America.

Since this lesson is about phrases like no sea que, how could I add "lest you burn yourself" to this sentence?

You can just attach the clause to the end: Usa la pinza para tocar ese carbón ardiente, no sea que te quemes. (Or you could use no vaya a ser que te quemes). Because these phrases express a negative precaution ("just in case [X bad thing] happens"), they always require the subjunctive mood, which is why we use quemes instead of the indicative quemas.

Why use ardiente for "burning" instead of a form of the verb quemar?

Ardiente is a specific adjective meaning "burning," "blazing," or "red-hot." It comes from the verb arder (to burn or blaze). If you used the gerund quemando, it would sound like an active progressive verb rather than a descriptive adjective. For describing a noun's physical state (a red-hot coal), ardiente is exactly the right word.

Is Usa in the present tense or is it a command?