Applying a urine bag involves several steps to ensure a proper and secure fit: 1. Clean the infant's genital area with a sterile wipe. 2. Peel the backing from the adhesive rim of the urine bag. 3. Carefully position the bag so that the opening is aligned with the infant's urethra. 4. Press the adhesive rim firmly to secure the bag in place. 5. Check periodically to ensure the bag remains securely attached and hasn't leaked.