Many soup recipes begin with a base of flavored broth or stock. Although both are now almost thought to be synonymous, purists still differentiate them. In addition, the way beef and veal stocks are prepared, whether or not their bones and vegetables are pre-roasted, will produce very different results. Hopefully the following discussion will offer some clarity. For convenience, I focused on chicken, beef, and veal.
At their cores, broth and the ingredients for stock are similar. They all start with chicken, beef, or veal. They incorporate vegetables, herbs, seasonings, and water. There seems to be a consensus among chiefs that broth's main ingredient is mostly meat. Stocks are predominantly made with bones and some meat; chicken wings, necks, backbones and legs are common as are beef and veal shins, shanks and marrow bones. There is little disagreement that the use of bones in stocks results in a deeper palate. Both maybe classically finished in a "bain marie", slow simmering water for 4 or 5 hours along with all other ingredients. However, the basic quick stock recipe below can be rapid boiled in a little over an hour.
For bolder versions of stock, bones and vegetables are caramelized in a roasting pan and the pan is deglazed before everything is placed in the simmering water. This technique makes the richest and deepest stock. It is also used to make flavorful sauces that are especially complimentary with brasher meat dishes. If not hardy enough, some cooks also add tomato paste for even more intensity and richness. There is something magic about concentrated tomato in stews and stocks.
Vegetables, the French commonly use a mirepoix, a mixture of diced or sliced carrots, celery and onions. Italians use a Battuta with the same trio. However, Italians apply them more like a spice, finely chopping or mincing. Conceptually mincing improves taste absorption. For additional flavors, Italians might also incorporate pancetta, slices of an unprocessed bacon roll along with the three vegetables. Leeks and garlic are also common.
Herbs and spices, parsley, thyme, ground pepper, peppercorns, bay leaf and Tuscany seasoning are frequently incorporated.
Store bought broth may not have the depth of flavors homemade have but there are easy ways to give them credibility, pumping up their flavors. Soups incorporate additional cooked flavors like chicken, beef, mini meatballs, carrots, celery, onion, garlic, herbs, eggs, peas, tortellini pasta, or parmigiana cheese. Soups with hardy ingredients like lentil soup (recipe below) uses broth in a supportive role adding flavor not designed to be dominant.
When using store bought broth as a base for soup, I prefer reduced salt. I also avoid added salt. Instead of adjusting seasoning with salt at the end, I use Organic "Better Than Bouillon™". Jars are available in chicken, beef, vegetable, fish, etc. flavors. I use it sparingly as I would salt. It salts the soup while contributing additional intensity of broth flavors. If you decide to try it, I'd love to hear your feedback.