Match an Existing Grid: Select a to match. The grid dimensions and grid extents will be used from the selected grid. When this option is selected, all other fields on the page will be grayed out and cannot be edited. This is a good option when you are planning on performing grid calculations.

Create New Grid: Allows you to enter the grid extents and dimensions of the new grid.

Compute Extents: This option will look through all of the data that is to be used in the gridding process for the minimums and maximums of the X and Y fields.

Clear Overrides: This will clear any overrides that the user has defined. The grid will be the minimum bounding rectangle of the selected data.

Constrain Z Extents: This option allows you to specify that when gridding, to constrain the Z values to those specified. Some gridding algorithms, such as minimum curvature can greatly exaggerate the values, especially when the seed points are not spread out evenly. 

Column width and row height: Select the width of each column and height of each row for the new grid. When changing the size, the number of columns and rows will be updated.

Number of columns and rows:  Select the number of columns and rows the new grid will have. When changing the columns and rows, the column width and row height will be updated.