How to add the value of User Input to value of in A Cell???

Hi everybody,

So I have been trying to make this vba excel sheet for keep track of my expenses and it works pretty well but, I am stuck on an aspect of my code. I'm trying to take the data that the user (my wife) from a text box and then add that value to a value in a cell. I know how to add cells when just using the excel sheet but I don't know how to write the code to do this from a textbox. Any help would be greatly appreciated! Thank You.
I would insert image but, for some reason it won't let me??