While hair serums are mostly applied to damp hair after a fresh wash, some serums can also be used on dry hair.
When using it on wet hair, take a pump of the serum on your palms, rub them together and gently apply along the length of your hair, working your way up from the tips to the middle. Avoid applying the product to the roots or using too much of it, as it can make your hair look limp and greasy. Comb your hair once done and style.
As for using it on dry hair, you can lightly spritz some product onto the strands of the hair for a beautiful sheen.