How many days do you start counting from the day of possibly being in contact with someone who tested positive with covid?

Basics: A covid carrier is considered contagious from 2 days before to 7 days after the onset of any symptom. How that applies in your case is hard to predict given the lack of specific contact information (when, direct or indirect contact, duration of contact, etc.).

Isolation guidelines: Count from the day of exposure. If you're not tested, and no symptoms isolate for 10 days, but 14 days would be better. If symptoms present, isolate for 14 days and no symptoms for at least 3 days. Practice mask wearing and social distancing when appropriate.