DOUBT IN AFL PLOT SHAPE FUNCTION

hy i am a biginer in afl .,when i learn afl i am stuck in this lines

PlotShapes(IIf(Buy, shapeSquare, shapeNone),colorGreen, 0, L, Offset=-40);
PlotShapes(IIf(Buy, shapeSquare, shapeNone),colorLime, 0,L, Offset=-50);
PlotShapes(IIf(Buy, shapeUpArrow, shapeNone),colorWhite, 0,L, Offset=-45);

why three lines for buy shape?
what is the meaning of " , 0, L, Offset=-40);" these three?
please help

@sarathlal There is a user guide that explains everything. No you do not need three lines.

https://www.amibroker.com/guide/afl/plotshapes.html

Clearly explained in the user guide. And you can see many examples in the User Library listed if you scroll down that page.