Does nano urea actually work and how do I spray it correctly?

Nano urea is a foliar (leaf-spray) nitrogen product, not a replacement for the basal soil fertiliser you put at sowing. Think of it as a supplement to top up nitrogen, mainly during active growth stages. To use it well: shake the bottle, mix it into clean water at the rate printed on that specific product label (different brands and pack sizes have different dilution, so follow the label, not a neighbour's guess), and spray on the leaves with a fine nozzle so it coats the foliage evenly. Spray in the cool hours, early morning or late evening, not in strong afternoon sun, and avoid spraying right before expected rain so it does not wash off. Generally two well-timed foliar sprays at the right growth stages give the best response. Whether it can replace part of your soil urea depends on your crop, soil and how the crop is growing, so treat it as a tool that may reduce, not fully remove, your urea need. Follow the product label and your local KVK advice for your crop, match the overall nitrogen to your Soil Health Card or soil test, and do not over-apply.