Follow these steps:
If you Grid Inside data, only the data which falls within the polygon will be used in gridding. Grid Outside will grid only the data that falls outside of the polygon area. See examples below.
When you use a polygon to limit data for gridding, the data points specified by the polygon will be displayed in the Kernel Gridding window. You may arrange your grid geometry as you like.
Gridding will be done using only the specified data. After gridding, all grid nodes in the area excluded by the polygon are dropped.
What do you want to do?