With our dietary restrictions, this skill can be quite useful as there will be no preservatives and you can include only ingredients which you know to be bladder friendly for you. I've found it's easy to do once you get the hang of it. It's fun to experiment with and it has a richer flavor (and less salt) than store bought.
The following is just a basic method rather than a specific recipe. The ingredients will depend on what you have on hand and what's available where you live. If you haven't made your own stock before, there is a lot of information on the internet or in cookbooks that you can browse for more tips before you start.
You can use any combination of vegetables, fresh herbs, and clean, edible vegetable scraps (broccoli stems or carrot tops, for instance) that you desire.
For a classic base, saute carrots, celery, and onions together for a few minutes. If you avoid onions you can just use carrots and celery, plus garlic (whole cloves) if you wish. Transfer to a large pot and add the rest of your ingredients.
Add enough water to just cover the vegetables. Add salt (to taste - I usually use 1-2 teaspoons).
Bring to a boil and then simmer. Length of time is up to you - I usually simmer for about 45 minutes.
Remove from heat and allow it to cool for a little while with the vegetables in the pot. Then strain all the vegetables out by pouring it through a strainer or colander into another pot or a large bowl. Discard vegetables in the compost.
The liquid broth is now ready for use in soups and sauces. It will keep for a few days in the fridge or longer in the freezer.
Good in stock (examples): sweet potato, rutabaga, parsley (including stems), lovage, bay leaf, zucchini, turnip, fresh thyme including stems (in a loose leaf tea bag), celery (including heart and leaves), carrots (including clean peels or leaves).