Hello Rahmat Awaludin,

For exporting data in v7 you need to apply import & export configuration from settings. than you will be able to export data.

Steps to set the configuration:

Step 1: Go to Setting >>Configuration>>General Settings

Click on General setting than you this below screen will appear.

Here you can see Import/Export confiuguration. check this box and click on apply botton on top of the screen than import & export option will be avail. in all objects.

after this configuration is done you need to select the records which you want to export . when records will be selected than export action will be appear in More .

Hope this will help.

Regards, Anil R.K.(SerpentCS)

If you use Odoo v8:

Step 1:
Go to Sales > Customers. Select the checkboxes of the lines you want to export. Click "More". Click "Export".
http://imgur.com/JsLE7U0

Step 2:
Select all the info you want to export, click "Add", then click "Export" - DONE! :-)