The example shows the client selection built-in feature of Telerik RadGrid. Single row can be selected by clicking the row itself (note that you need to set AllowRowSelect="true" to enable client row selection). There is also a GridClientSelectColumn, which you can use to select and unselect row(s) client-side. You can use it to select all the rows using the check box at the header.

Furthermore, you can select multiple rows after setting the AllowMultiRowSelection property of the grid to true. Several rows can be selected either by:

• holding the Ctrl key when clicking the rows
• dragging a region with the mouse to select all underlying rows. To accomplish this task you have to set the ClientSettings -> Selecting -> EnableDragToSelectRows property to true.
• clicking a row, holding the Shift key and clicking another row upwards/downwards

Later on, you can unselect a row by holding the Crtl key and clicking the row. You don't need this if you have GridClientSelectColumn added.

The selected items will be available through the SelectedRows client collection of the respective RadGridTable.

Note: When you select a grid row server-side on initial load and want to deselect that row on user client selection, you should set the ClientSettings -> ApplyStylesOnClient attribute of Telerik RadGrid to true.

Finally, there is also a checkbox column (called GridClientSelectColumn which displays a checkbox control for each item in the column. This allows you to select grid rows client-side automatically when you change the status of the checkbox to checked. Additionally, if you choose AllowMultiRowSelection = true for the grid, a checkbox will be displayed in the column header to toggle the checked/selected stated of the rows simultaneously (according to the state of that checkbox in the header).

Further details about the client selection of Telerik RadGrid you can find in the Selecting grid items help chapter:
Selecting grid items