Can I back up my MacBook air to the iCloud?

stice4ken wrote:

Taking my MacBook Air in to Genius Store appointment and want to back-up the device on the iCloud.

How do I do this?

iCloud is not a computer backup mechanism. iCloud provides file synchronization across devices accessing the iCloud account. Use Time Machine to backup your computer data to an externally connected drive.

See here for instructions on how to prepare your Mac for servicing:

How to back up your Mac - Official Apple Support

Time Machine does not backup to iCloud like iPhones and iPads do.

Backup to a dedicated external HDD or other as suggested in the referring article. The HDD is entirely sufficient..

For sure, you'll want to get an external hard disk (2x the size of your Mac's hard disk is recommended). Then, as was stated earlier, back up your Mac to this external drive using Time Machine.