//Make all text fit the cells
worksheet.Cells[worksheet.Dimension.Address].AutoFitColumns();

//Autofit with minimum size for the column.
double minimumSize = 10;
worksheet.Cells[worksheet.Dimension.Address].AutoFitColumns(minimumSize);    

//Autofit with minimum and maximum size for the column.
double maximumSize = 50;
worksheet.Cells[worksheet.Dimension.Address].AutoFitColumns(minimumSize, maximumSize);

//optional use this to make all columms just a bit wider, text would sometimes still overflow after AutoFitColumns().
for (int col = 1; col <= worksheet.Dimension.End.Column; col++)
{
    worksheet.Column(col).Width = worksheet.Column(col).Width + 1;
}

//Hide column "A"
worksheet.Column(1).Hidden = true;

//Hide row 1
worksheet.Row(1).Hidden = true;

//Set the row "A" height to 15
double rowHeight = 15;
worksheet.Row(1).Height = rowHeight;

//Set the column 1 width to 50
double columnWidth = 50;
worksheet.Column(1).Width = columnWidth;

When Bestfit is set to true, the column will grow wider when a user inputs numbers in a cell

worksheet.Column(1).BestFit = true;

workSheet.Cells[1,5,100,5].Copy(workSheet.Cells[1,2,100,2]);

Copies column 5 into column 2 Basically Source.Copy(Destination)

This would only copy the first 100 rows.

Cells[RowStart, ColumnStart, RowEnd, ColumnEnd ]
is the format so to copy a row into another row you would just switch the indexes accordingly