This is a leave-on exfoliating serum, designed for use after cleansing and toning on completely dry skin. The standard application order is: cleanser, toner (if used), this serum, moisturizer, and finally sunscreen in the morning. Apply a pea-sized amount (about 3-4 drops) to your entire face or just the T-zone if that's your target area, avoiding the immediate eye contour.
As for frequency, there is no one-size-fits-all answer. Start slowly, with once or twice a week, ideally in your evening routine. This allows you to monitor your skin's response without the added stress of sun exposure. If your skin looks and feels fine—smoother, less congested, with no irritation—you can consider increasing to every other night or even nightly, provided you do not use other exfoliating actives on the same nights.
Key signs to watch for: If your skin starts feeling tight, looks flaky, becomes unusually shiny (a sign of a compromised barrier), or shows persistent redness, you are likely over-exfoliating. In that case, reduce frequency immediately, focus on hydration, and let your skin recover. Consistency with a frequency your skin can tolerate is far more beneficial than aggressive, daily use that leads to irritation.