Creating a Google Cover Image should be very easy. If you don't have Photoshop you can use this free online image editing program: coverphotoeditor.com, to create your Google cover image.

If you do have Photoshop, here's a Google+ cover template:

Click the image to view it at full size.

Uploading your Google+ cover image to your profile:

1. log into your Google+ account.
2. Click on the 'profile icon on the left.
   
3. Click the blue 'Edit profile' button at the top of the browser window.
4. Click on the row of images where it says 'Change Photos'.
   
5. Choose the left icon where it says 'Choose a template:'.
   
6. Click on  'Change cover photo.'.
7. Navigate to a directory on your computer where you have a landscape image you want to use as a cover image. Keep in mind your image has to be at least 940 pixels tall and 180 pixels wide.
8. Select and upload the image.
9. Drag the corners of the cropping to where you want you image to be cropped and press the 'Save' button.
10. Click the 'OK' button.

You should now see your Google+ cover on your profile.