Generally, if you put into Google 'how do I....in Excel" you will be able to copy and paste the formula.
There is a standard form in Excel and once you learn that, it makes it easier to understand why the formula works.
Every formula starts with '='. Every cell in the spreadsheet has a cell reference, which is the column letter and the row number. So B2 is second column, second row.
When you use a formula to add two cells together, you can type '=A1 + B2', for example. If you copy and paste that formula, though, it will change A1 and B2 as it goes down, so the next line would read "=A2 + B3". If you don't want that, you put a $ before the bit you want to keep the same. So "=$A$3 + B1" means that the cell referenced A3 would always be used, and the cell that is added to it would change.
IF compares a cell against a statement and you give two outcomes. So a classic one is when you want to make your spreadsheet neat. You can type =IF(ISBLANK(D2),"","Sum(D2 + C1")
That's saying:
"Check if the cell in the 4th column and 2nd row is empty. If it's empty, leave this cell empty. If it isn't empty, add the number in the 4th column and 2nd row to the number in the 3rd column and 1st row, then show that number here."