The general purpose of a pivot level is, as the name suggests, to identify a kind of “balance point” from the previous period¨s price range. In an uptrend, if the current price is trading above this balance point, or pivotal line then one can assume that the trend is still continuing, as vice versa.
But there are various ways of calculating this pivot point. E.g. the average of the high/low from previous period, or the ave of H/L/C or O/H/L/C and, of course, these all give slightly different values for the pivot. The idea here is to give varying weightings on the final value.
In addition to the actual pivot line, there are usually also a range of Support and Resistance lines which are also calculated on various formulas using some the values of the previous OHLC values. The values of these R1,R2,R3,R4 and S1,S2,S3,S4 etc are also different depending on the type of pivot being used.
You will find a lot of information about these on the Internet including this from Babypips:
Hope this helps a bit!