Aniline dye is sold in powder form, to be mixed with water, alcohol or both for application. Many professionals use water-soluble dyes for overall color, because they go on evenly and maintain their integrity well; alcohol-based versions dry faster but don't hold their color as reliably. Dye powders come with instructions for mixing amounts and methods. You can tinker with the color by adding a little more to intensify it or a little less to lighten it.
Apply the dye to unsealed wood with a brush, a foam applicator or a sponge. You'll probably need two to three coats unless you want the color to be very sheer. Allow at least 12 hours for drying between coats. Apply a clear sealer as a finish coat to preserve the dye and add shine.