Does my iMac automatically back up to icloud

Your iPhone and iPad will back up to iCloud if you enabled it. See: iCloud: Backup and restore overview

Your Mac can use iCloud Drive to store documents and data, if you select to store them there, but that is not a backup.

The easiest way to routinely back up your Mac is Time Machine. Mac Basics: Time Machine

Basic Backup

For some people Time Machine will be more than adequate. Time Machine is part of OS X. There are two components:

1. A Time Machine preferences panel as part of System Preferences;

2. A Time Machine application located in the Applications folder. It is

used to manage backups and to restore backups. Time Machine

requires a backup drive that is at least twice the capacity of the

drive being backed up.

3. Time Machine requires a backup drive that is at least double the

capacity of the drive(s) it backs up.

Alternatively, get an external drive at least equal in size to the internal hard drive and make (and maintain) a bootable clone/backup. You can make a bootable clone using the Restore option of Disk Utility. You can also make and maintain clones with good backup software. My personal recommendations are (order is not significant):

1. Carbon Copy Cloner

2. Get Backup

3. Deja Vu

4. SuperDuper!

5. Synk Pro

6. Tri-Backup

Visit The XLab FAQs and read the FAQ on backup and restore. Also read How to Back Up and Restore Your Files. For help with using Time Machine visit Pondini's Time Machine FAQ for help with all things Time Machine.

Although you can buy a complete external drive system, you can also put one together if you are so inclined. It's relatively easy and only requires a Phillips head screwdriver (typically.) You can purchase hard drives separately. This gives you an opportunity to shop for the best prices on a hard drive of your choice. Reliable brands include Seagate, Hitachi, Western Digital, Toshiba, and Fujitsu. You can find reviews and benchmarks on many drives at Storage Review.

Enclosures for FireWire and USB are readily available. You can find only FireWire enclosures, only USB enclosures, and enclosures that feature multiple ports. I would stress getting enclosures that use the Oxford chipsets especially for Firewire drives (911, 921, 922, for example.) You can find enclosures at places such as;

1. Cool Drives

2. OWC

3. WiebeTech

4. Firewire Direct

5. California Drives

6. NewEgg

All you need do is remove a case cover, mount the hard drive in the enclosure and connect the cables, then re-attach the case cover. Usually the only tool required is a small or medium Phillips screwdriver.