Use the category to set your plans. At Good and Moderate, most people can be active outdoors. At Unhealthy for Sensitive Groups (orange), sensitive people should cut back on prolonged or heavy exertion; by Unhealthy (red) everyone should, and by Very Unhealthy/Hazardous, move activity indoors and keep it light.
Indoors, keep windows closed when outdoor air is bad and run a HEPA air purifier sized for the room; a well-fitted box-fan filter is a low-cost alternative during smoke events. Avoid adding indoor pollution — frying, candles, incense and vacuuming without a HEPA filter all raise PM2.5.
If you must be outside in unhealthy air, a properly fitted N95 or FFP2 respirator filters fine particles; cloth and surgical masks do little for PM2.5. Reduce exertion, choose routes away from busy roads, and shorten your time outdoors.
Wildfire smoke is mostly PM2.5 and can push the AQI into the purple and maroon ranges far from the fire itself — check the responsible pollutant and the smoke outlook, not just the headline number, and revisit guidance through the day as winds shift.