Checking new device serial number

Yes, it's ok. You will need to receive the MBA and finish its setup.

Since you asked, review Set up your MacBook Air - Apple Support. Might as well get ready. Should you require any assistance whatsoever, you can contact Apple, here: Official Apple Support. Setup assistance for new Macs purchased directly from Apple is complimentary.

If you ordered this On-Line and from Apple

Log into your the Apple Store with the account you used to make this purchase

Look for the heading called Orders

This should bring up all your current orders including this recent purchase

Once found, in top right os screen

Look for " View Invoice "

In My Invoice

The Serial Number appears

Have redacted the serial number as we are not permitted to reveal personal information