A function argument is a specific input to a function. For example, the VLOOKUP function takes four arguments as follows:
=VLOOKUP (value, table, col_index, [range_lookup])
Note most arguments are required, but some are optional. In Excel, optional arguments are denoted with square brackets. For example, the fourth argument in VLOOKUP function, range_lookup, is optional and appears in square brackets as shown above.
Finally, many Excel functions accept multiple optional arguments, which are denoted with an ellipses (…)
For example, the COUNTIFS function accepts multiple and optional range and criteria pairs, which can be represented like this:
=COUNTIFS(range1,criteria1,[range2,criteria2],...)
This means you can optionally add additional arguments in pairs: range3/criteria3, range4/criteria4, etc.
The function screen tip is a small window that appears when you click into a function in the formula bar. Although this window looks quite simple, it is actually a very useful tool when editing and debugging Excel formulas.
When the function screen tip is visible, you can use it to precisely navigate the function arguments in a formula. The window is context-sensitive and its contents depend on the function the cursor resides in. As you move the cursor through a formula, the currently active argument is bolded. If the cursor is moved to a different function in the same formula, the arguments for that function are displayed.
If you click directly on the argument name, the text that makes up that argument will be selected. This is a powerful way to copy and paste into a formula without bringing in extra characters, or accidentally truncating an important character.
Finally, if the function screen tip window is in your way, you can move it to a new location using the four headed arrow.
