Yes, you still need sunscreen. This is an after-sun product, not a sunscreen, and it does not provide UV protection. Its purpose is to help skin that feels warm, dry or tight after sun exposure feel more hydrated and comfortable, not to block the sun's rays.
Apply sunscreen before going outside and reapply it according to that product's instructions while you are outdoors. Use the Biosun spray after you come in from the sun, after swimming, or after a shower when the skin feels dry, tight or overheated. If you apply it before going into the sun, it cannot protect you; you would still need a proper SPF product on top or instead.
A practical routine is to wear sunscreen during the day, then shower and apply the after-sun spray in the evening or whenever you are finished with sun exposure. The spray can cover large areas such as the shoulders, back, chest and legs, adding a light moisture layer and a cooling sensation. It does not replace your usual after-sun care or any treatment your doctor recommends.
If you notice persistent redness, stinging or blistering after sun exposure, do not rely on after-sun cosmetics alone. Ask a pharmacist or doctor for advice.