This filter is all about the liquidity of an instrument. It looks at an instrument's “average currency volume” for the past several days/months (that you specified), and if it's greater or less than the “average currency volume” that you you specified, the instrument will be bought (or sold).

“Average currency volume”, also known as “Dollar Volume Liquidity” is not just the number of shares traded (its volume); it is actually the volume multiplied by the share's unadjusted closing price. This is then averaged for the past period of time that you specified (e.g the average of the past 30 days). So, the “Average Currency Volume” is specified in dollars, not volume.

This filter is useful, for example, if you don't want to trade stocks that have low liquidity; such stocks' positions are generally difficult to enter or exit, which may cause huge slippage and loss of unrealized gain. But you can also look for lower volume stocks if you wish so; they may provide faster growth than the larger volume stocks. Of course, what dollar volume you're looking for depends very much on your account size; you don't want to trade on low liquidity instruments if you have a larger account.

1.  The first Parameter defines the time period to calculate the Average Currency Volume. Let's say you want the average of the past 30 days, then enter 30 days here (type 30 and choose from the dropdown either Days or Months). 

Longer period gives a more accurate estimate, but if you're a short-term trader adjust this accordingly (you don't want outlier liquidity to be considered).

2.  The second Parameter defines whether the average must be “Greater than” or “Less than” the dollar volume that you specified, for the instrument to be considered. 

You can also decide whether the average must fall “Between” or “Not Between” (outside) the maximum and minimum dollar volumes that you specified on the third and fourth parameters that show up.

3.  The third and/or fourth parameters define the threshold dollar volume.