First, apply a polyurethane thick layer where you want the glitter. Use a round paintbrush to paint on.
Pick which glitter you want. There are many different types. You can choose from flakes, sand, or medium. No limitation to what type of glitter you use.
Next, pour glitter on your painted line. Put a generous amount of glitter all the way along. Don't be afraid to cake it on there. You will save this glitter so don't be scared. Give your board a tap to move the glitter around so it gets in all the places.
Once all dried shake off your excess glitter and save it and pour it back into the bottle. Don't waste your glitter.
Optional step, but highly recommend: Use polyurethane clear spray to seal the glitter, so that it doesn't flake off easily and it'll make your glitter accents last longer.
Video
Notes
NOTE: I recommend waiting 24 hours before cleaning off the excess sand, so it gives everything enough time to dry.