Start by boiling your water. You will need to blanch and prepare your tomatoes before you can do anything else. Make sure you cut out any bad spots in the tomatoes as you chop them.
Place your tomatoes gently in the boiling water and let them cook for a minute. You’ll know they are ready once the skin starts peeling off.
Put them in an ice bath (or large saucepan of cold water) to cool, and allow them to fully cool before you start to peel - this is an easy way to get a steam burn, otherwise!
Peel each tomato and cut it into fine pieces. If you’re like me and want to expend as little effort as possible, you can also just squeeze or press them into a stock pot.
You will also need to cut up your peppers and onions.
Put this large pot back over the heat. Add your other ingredients (vinegar, garlic, etc.), including your diced peppers and onions.
Let this simmer and cook down for a bit while you prepare your jars and canners. I recommend tasting the salsa as it’s cooking to make sure it’s at the desired level of heat.