How to print check box in ALV list display and how to pick selected ones

Hi

i am displaying one ALV list dispaly. for that im adding one check box fields by filling the fieldcat as below:

wa_fldcat-checkbox = 'X'.

wa_fldcat-edit = 'X'.

but the check box is showing disable mode only. i want to display that check box and if i select that check box i want pick that records. for ALV grid i found one FM to pick records of selectedones as below.

DATA ref_grid TYPE REF TO cl_gui_alv_grid.

IF ref_grid IS INITIAL.

CALL FUNCTION 'GET_GLOBALS_FROM_SLVC_FULLSCR'

IMPORTING

e_grid = ref_grid.

ENDIF.

IF ref_grid IS NOT INITIAL.

CALL METHOD ref_grid->check_changed_data.

ENDIF.

but how can i do for list display to pick those selected one records.

Can any one sugget regarding this.

Thanks in advance.

Rahul.