Return on investment is the gain divided by the amount invested. The gain is the number you enter, or the ending value minus the starting value when those are the fields. The result is a percent. It is not a compound annual rate unless the period is one year and nothing else changed.
A $10,000 investment that produces a $2,000 gain has a 20% return. That 20% does not say how many years it took. For a multi-year rate, use the CAGR page.
Fees and taxes are already out of the gain only if you subtracted them before typing it. The page does not project a future return.