It's very easy, but can be a bit messy with some projects.
1. After cleanup sanding, I spray three fairly heavy coats of MinWax clear satin polyurethane from spray cans and let each coat dry enough to handle it between coats. Allow to fully dry overnight in a room temperature part of your house where the smell isn't objectionable.
2. Using a 3/8" or smaller artist brush, coat the area to be colored with General Finishes Java Gel Stain. Let it dry about 15 minutes.
3. I tear some paper towels in half or in thirds depending on the size project I'm working on. These will be used to selectively remove some of the gel stain to make it look like it has an old rustic look, or blackened from a torch flame treatment. The paper towel material can be folded as needed, with either side being wet with a little oil based paint thinner on it to partially wipe off, or fully wipe off the gel stain. You can always selectively re-paint the gel stain where you removed too much of the gel stain unintentionally.
4. When it looks satisfactory to your wishes, let the gel stain dry, then spray a final coat of clear satin polyurethane over the gel stain. Two coats if you want more protection.
This project took around 45 minutes to dark stain because I had to paint the 3d modeled text by hand with a very small point artist brush. Practice using this method and you can get pretty good results with it. I use it a lot now, and the recent Aztec-Mayan theme guitar I posted here is one of my best applications for it to date. I've gotten a lot of "Oh WOW!" remarks for this door sign and the guitar when people see them first hand.