I am a teacher. After a simple tooth extraction, how many hours should I rest before teaching or testing (orally) again? When can I eat regular food again? I shouldn't use straws for how many days? How many days avoid cold/hot drinks & hot/spicy food?

Don'b be a hero. Take the day of surgery off from work. You need time for bleeding to stop, for the anesthesia to be metabolized, and to use cold compresses to minimize swelling. Follow your Dentist or Oral Surgeon's verbal and written instructions to the letter. Soft high-protein diet for a few days, then gradually titrate yourself back to your normal diet. For about a week avoid very hot, cold, spicy.
Post op Extraction. Always best to ask the dentist who actually treated you. As a general rule- A few hours minimum when anesthesia has worn off and bleeding has stopped. Next day should be fine. Depends what you mean by regular food but a few days minimum, perhaps a week. No straws for a few days minimum, perhaps a week. Cold, hot and spicy foods as you can tolerate them, preferably not the first couple of days.