Having a well made, highly flavored stock is an essential building block in the kitchen. Stocks can be used for creating sauces, soups, and adding flavors to other dishes. Store bought stocks and bouillons vary in quality and are often highly salty, not to mention potentially full of some ingredients that are unpronounceable. Scratch made stocks contain more nutritional value, and taste better. Vegetable stocks are much trickier to achieve full flavors with than animal based stocks. One of the keys is using a variety of LOTS of vegetables to make your stock. This could get expensive if you were to go out and buy all the vegetables needed, but there is an easy cheap way to make vegetable stock for close to free.
I keep a resealable bag in the freezer and gradually fill it full of veggie trimmings. When the bag is full I make a batch of stock. Simple, and uses up bits of food that would otherwise be wasted. The other great thing about it is the diversity of flavors from the variety of veggie and herb bits. I take almost everything kind of veggie or herb in my stock freezer bag except potatoes. Things you might not think of to put in: herb stems, onion skins, garlic bits, tops, cores and stems of any type of vegetable (particularly mushroom stems). Mushroom adds a depth of flavor or, umami taste to your stock. If you are going for a certain stock colour than you might want to consider the colour of veggies you add. My stock always comes out brown ‘ish’.

Ok now for the method:
I find that one lg freezer bag full is often perfect for my stock pot (it’s a pasta pot, but its the biggest pot I have which works). Dump the bag of veggies in the pot. I then add mirepoix (carrot, onion, and celery) unless there are lots in the frozen veggie mix. Just break/chop them up and throw them in chunks. You can add spices as well. If you know what you are using the stock for you can add additional flavors accordingly. For a generic stock I usually go with 10-12 whole peppercorns, a few smashed cloves of garlic and a bay leaf.But for example if I know I’m making an Asian style soup I might add a star anise, some lemongrass and a piece of ginger (or something like that), It’s up to you. Then cover the ingredients with water, leaving a few inches of space at the top so it doesn’t boil over.
Turn on the burner to md to get it started, and once the stock gets going turn down heat to maintain a simmer, usually md-low. Simmer for a few hours until all the flavours are extracted and liquid reduces almost by half. Taste it to tell if it is ready. Strain all the vegetable/herb/spice matter out of the stock. Those items are now super mushy and exhausted of flavour and nutrients so they are not good for much except the compost. You are now ready to use your stock for whatever you like!
If you aren’t using it right away you will need to cool it down quickly to store it. I will freeze my stock in different sizes. A few in ice cube trays for flavoring, and then lg containers for making soups. I don’t have much freezer space though so I often make it as needed. It can last few days in the fridge. Don’t put steaming hot stock into your home freezer or fridge, it can raise the temperature inside it and potentially create conditions for bacteria to breed. That’s why it’s important to get it reasonably cool first. I usually separate it into smaller amounts, and/or you can make a cooling wand. Take a water bottle and freeze it full of water. Then use it to stir stock to cool it down quickly and evenly. Also always reheat soups to a boiling point before eating them just in case.
Congratulations!!! You have now just passed vegetable stock 101. On to create soups and sauces galore!