You can use both numbers and cell references in formulas.
No. You can have formulas that just use numbers, though for those it is better to put the numbers into the cells and refer to the cells. There are also some functions that do not refer to cells, like the TODAY() function.
If you put numbers direct into formulas then the formulas are very restricted. They can only work with the specific numbers you have. If you want to use other numbers, you have to keep changing the formulas. It is better to use cell references in the formulas. Then all you have to do is change the cell values and the formulas will automatically calculate the new totals. It also makes it possible to copy the formulas so that they can use many sets of numbers, all through the same original formula. If you wanted to add 10 pairs of numbers, you could write 10 individual formulas each with the numbers you want to add, or do one single formula and copy it and it will add all 10 pairs. If numbers are in cells you can see the values on the sheet, which you can't do if they are all in the formulas. So if the numbers are separate in cells, it is easier to understand what is going on. For these and many other reasons, we use cell references rather than values in the spreadsheet formulas.
If you type formulas with numbers directly into them, then every time you make changes to the spreadsheet, you will need to directly change the formulas too. It also makes them more difficult to copy. It also means that you will not see the figures that are in the formulas, just the result. If a formula references a cell, then you can see the figures that are used and the cells can be changed without having to adjust the formulas and the formulas can be copied to other cells and will look at the correct cells to do other calculations. For those and other reasons, you use cell references and not numbers in formulas where possible.
Yes. Formulas can contain all sorts of things, including absolute and relative cell references.
No. Most formulas would not use them. It is used when you want to have a formula that is to be copied, but has a cell reference in it that you don't want to change when it is copied. For a lot of formulas that is not a requirement, so absolute cell reference are only used in some formulas.
Sure, a cell can be referenced by name. In MathCAD, the "spreadsheets" depend on location and defined variables. They do not use RC references at all.
Where possible you should always use cell references. It makes things a lot easier when you are changing or maintaining a spreadsheet. Even if you are using the exact same value in all of a set of formulas, you should put that value into one cell, and use an absolute reference in the formula to reference it. If formulas have cell references in them, then when figures change, you do not have to redo all the formulas. You just change the relevant figures and the formulas will all recalculate them.Values.
You use formulas rather than actual numeric values. Logical values are usually generated from formulas, so they are rarely typed in literally, so you would type formulas in instead of them, with cell references in those formulas, and possibly some values.
Horizontal references in Excel refer to a method of referencing data in a row. This means that data is organized in rows and referenced using row numbers. Horizontal references allow you to use formulas to work with data across an entire row instead of just a single cell.
Yes. They also include some specialised functions to do some of those activities, the most common being the SUM function.
Because it gives a spreadsheet more flexibility. For the type of things that spreadsheets are used for, figures change frequently. In order to deal with this, formulas would have to change when changes are made to values if values were put directly into formulas. By using cell references then the formulas can do the calculations whatever values are in the cells. This speeds up the spreadsheet, as you may only have to change one value and this can then change a whole range of totals. So you can very quickly see the effects of changing values, without having to rewrite formulas. Using cell references also means formulas can be copied and so deal with other combinations of cell references.
Many different functions can perform calculations or operations. Excel comes with hundreds of them. They can be accessed by clicking on the fx icon. The most commonly used function is usually the SUM function. It is generally used to add a range of values, but it can be used to do other kinds of calculations. It can be accessed by clicking on the Σ character on the toolbar.