Step 3: Add the atoms

Now we will add the Na and Cl atoms:

Make sure periodic display is turned off
Select the Sodium (Na) element tool from the periodic system
   that appears when you click the 'X' element on the toolbar

After this you see at the bottom of the screen "Na tool" in the status field:

Click once in the drawing area, near the origin
Click once on the created atom to stop bonding

As you can see the atom is not exactly in the origin. This can be fixed if you wish:

Use the 'Set Origin' command from the 'Edit' menu

To add the Cl atom you can proceed the same way.

Select the Cl tool
Click once somewhere in the unit cell
Click on the new Cl atom to stop bonding

Next you should edit the Cl coordinates and change the Cl color:

Change the Cl coordinates to be (2.75,2.75,2.75) in the 'Coordinates' panel
Turn on periodic display (in the 'View' menu)

Now your system looks like: