In your opinion, what are a few of the most useful functions in Excel? How do you use them?

good question.

honestly, the answer is depended on what kind of work you are doing?

I mean, what you are doing with Excel?

In general, there is the common functions in (math, conditions, simple statistics, string, date, ...)

math: sum, power, ...

conditions: it, countif, sumif, ...

statistics: average, sdev, mean, ...

string: mid, left, right, ...

date: today, adddate, emonth, ...

it is a long list.

If you know what you want, you can find the right tool in Excel.