Excel has excellent help functions on how to set up formulas, link data from different pages to another, etc. I am sure google sheets is the same as far as doing their best to be user-friendly. There are also budget templates available. You will need to decide with her how you are going to split costs like rent, insurance, utilities, and other items you both benefit from. Usually it is fairest to compare net pay of each to combined total net, and use that percentage (whether it is 50-50, 60-40, or whatever) applied to mutual expenses. So if she makes 60 percent and you make 40 percent, she would pay 60 percent of rent and you would pay 40. OR you decide that you each would pay, say, 30 percent of your net pay toward rent, which would then tell you how much rent you can afford to take on.
My other advice is not to nickel and dime discretionary expenses, and keep your money technically separate though you might want a single joint checking account into which money for share expenses goes.