Put the sliced jalapeños, garlic, and onion in the 2 qt jar.
In a separate bowl, combine the water with the salt until dissolved, and then pour that solution in the 2 qt jar with the jalapeños until they are completely submerged. (If you can't keep them submerged, put a smaller jar in the mouth of the larger jar to get them to stay down, then cover with a cheesecloth and rubber band.
Place the canning lid and ring loosely on the jar, and let the jar sit in a quiet place in your kitchen or pantry undisturbed for 10 days.
If your goal is pickled peppers, then let sit on the counter for 72 hours.
After 10 days, pour your peppers and the brine into your blender and blend - if you are looking for a strained hot sauce, then strain through a fine mesh strainer or cheesecloth and store in hot sauce bottles that have been washed, or wine bottles work well too.