A good starting point in your quest to make a home budget, is to take stock of your current and recent situation, and list out all your monthly outgoings. If you only do this from memory, there is a chance you will miss one or more important items. You probably have several sources of information on what those regular outgoings are, and whether they are easy to find depends on how well organised you are with your paperwork. It is worth checking back over at least three months bank and credit card statements, and jot down what your regular payments are out of those. At the same time, you can also make a note of items of expenditure that may recur later on.
Overall most people tend to learn better this way rather than trying to learn all Excel formulas at the same time as this can be very confusing. Most of us tend to learn in smaller packages of information and you should look for a course of instruction that will allow you to do this. As you are learning to use Excel you should of course start by learning to use the formulas that you are actually using or are likely to have need of in the immediate future.