Experienced Excel users will appreciate that textboxes default to having a border and white background. That‘s because they are often used to add comments or guidance to a user and so have to stand out. Otherwise a user would be foolish not to type words directly into the spreadsheet‘s cells. As equations can only be created in textboxes, the default settings are somewhat different; there is no border and no fill.
You will find that there are dozens of different tutorials available online, ranging from books and courses that you can pay for to tutorials and video lessons that can be downloaded for free. Each of these courses is broken down into sections that will address each of the different sections of formula so that you can learn them in groups. This tends to make it much easier to fully grasp the necessary formula for each section before moving on to the next segment.