Nebulizers solution

Started using a nebulizer as a recommendation of my vocal coach for a play. Anyone has any experience with nebulizers and know the type of solution i have to use with it, and if i have to buy or mix it myself? I know to avoid tap water, and that its supposed to be a saline solution, but i dont know the ratios, if i can make it myself, or if i need to buy a specific one

Sorry for any english mistakes, english is not my first language :))