No Google API key is required.
To configure this module, you will need your CSE's alphanumeric ID ("cx"). Go to your CSE manage page, click on control panel and then click on code. The only part you need is the cx value; to isolate it you'll have to copy/paste the code into a text editor.
The collapsed advanced settings on the settings page provide various customizations such as country and language preferences. For example, with the Locale module enabled, the Google CSE user interface language can be selected dynamically based on the current user's language.
- Unpack in your modules folder (usually /sites/all/modules/) and enable under Administer > Site Building > Modules.