Summarize:

Take a cup of vinegar, a cup of sugar, and 1 teaspoon of salt and mix them together in a small bowl. Then take a whisk or spoon and stir the mixture until the sugar has completely dissolved. This should take one to two minutes. Once the sugar has dissolved, set this bowl aside along with the radishes and onion. Take a glass jar, like an old jam/jelly pot or Mason jar, and place the sliced radishes and onion wedges into the bottom of it. Once everything is inside, take the vinegar, sugar, and salt mixture and pour it over the radishes. Make sure that there is a little bit of space between the liquid marinade and the lip of the jar. Also, when putting the lid on, make sure not to secure it tightly as you want to leave room for carbonation to escape. You can also add 6 heads of fresh dill weed or a tablespoon of pink/black peppercorn for extra flavor. You may have to place a weight or other item into the jar to keep the radishes submerged. For example, you can take a smaller jar full of water and put it into the jar to weigh the radishes down. After you've put everything together, you need to let the radishes ferment. Allow the jar to sit at room temperature for anywhere between six days to two weeks. While the radishes ferment, they may lose their vibrant color. However, the flavor should deepen and they should remain crunchy. Keep in mind that fermented radishes have a pungent odor that may increase the longer they are jarred.
Make a marinade. Put everything into a wide-mouth, pint jar. Let the mixture sit.