Add the Risotto Ingredients
Your recipe will probably specify when to add the ingredients depending on how much cooking they will require. A good time to start adding ingredients is after you've added a couple of cups of stock so the flavours will meld.
Add Ingredients at Different Times
You can also choose to add some of the same ingredient earlier in the cooking and some later, to have a mix of more and less cooked ingredients. This works well with e.g. mushrooms. Adding a couple of tablespoons of Parmesan cheese about 3/4 of the way through cooking will also enhance the flavour.