They could use it as some sort of gel and apply it to the wound. But it Resident Evil 5 it comes out as a type of spray.
They probably mash the herb into fine dust, and put it in a cointainer, add some water and then shake it and spray it over the wound. Some say that the first aid sprays that are used contain a trace amount of T-virus (enough to repair cells, but too little to act destructively) and that is why when you are bitten in the game you never transform.
--they probably smoke it(LOL) or they use it like normal real-life people. Crush it, then something else.