How do you determine High, Low, Close

Hello, please, I have a pivot calculator, but do not know how to determine the real high, low and close of a particular session. Also, which time frame do I use and when do I calculate (which session)?
I will be very glad later to get a detailed reply on this.

There are various opinions on which closing time to use depending on where you are located in the world. Some use the close of trading in their region. Some use the London closing time whether they live near this time zone or not because London is considered the most influential forex trading center. Some use the closing time depending on the currency pair they trade (i.e. Tokyo for JPY pairs, London for GBP, Frankfort for EUR). I use EST for New York closing since NY is 2nd to London in importance and because it ends the 24 hour trading period that starts in the Far East (Auckland, NZ) so that seems to represent a full day. Also helps that it is my own timezone.

But you can always experiment with timezones for OHLC and see if one works better for you than another.

Thanks very much for that. I will try to apply that by using the London session