Summarize this article in one sentence.
Click the Apple menu {"smallUrl":"https:\/\/www.wikihow.com\/images\/f\/ff\/Macapple1.png","bigUrl":"\/images\/thumb\/f\/ff\/Macapple1.png\/29px-Macapple1.png","smallWidth":460,"smallHeight":476,"bigWidth":"29","bigHeight":"30","licensing":"<div class=\"mw-parser-output\"><p>I edited this screenshot of a Mac icon.\n<\/p><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"http:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a><br>\n<\/p><\/div>"}, click Restart..., and click Restart Now when prompted. Do so immediately after your Mac begins to restart. You should keep holding down the keys during this time. You may also see a spinning globe appear here. As soon as you see the spinning globe or Earth icon, release the keys. You should now be at the recovery screen. It's a grey hard drive icon in the window. This is in the bottom-right corner of the screen. Click the attached hard drive's name in the top-left side of the page. This menu item is at the top of the Mac's screen. A drop-down menu will appear. It's at the top of the drop-down menu. You'll find this in the middle of the window. It's in the drop-down menu. This blue button is in the bottom-right corner of the window. Clicking it prompts your hard drive to begin backing up to the external hard drive. This can take several hours to complete. If you get a "Restoration Failed" error, turn off FileVault and try again. It's in the bottom-right corner of the window. Your original hard drive is now backed up to the new hard drive. Click the red circle in the top-left corner of the window. It's on the left side of the window. Doing so will restart your computer. Click the Apple logo in the top-left corner of the screen. A drop-down menu will appear. It's near the top of the Apple drop-down menu. This grey hard drive icon is in the middle of the System Preferences window. Click the lock icon in the bottom-left corner of the window, then enter your account password when prompted. Click the yellow attached hard drive's icon at the top of the window. It's on the right side of the window. Doing so will reboot your Mac from the new hard drive, which will ensure that the hard drive is usable as a bootable drive on any other Mac. This can take several minutes. To do so:  Open the Apple menu {"smallUrl":"https:\/\/www.wikihow.com\/images\/f\/ff\/Macapple1.png","bigUrl":"\/images\/thumb\/f\/ff\/Macapple1.png\/29px-Macapple1.png","smallWidth":460,"smallHeight":476,"bigWidth":"29","bigHeight":"30","licensing":"<div class=\"mw-parser-output\"><p>I edited this screenshot of a Mac icon.\n<\/p><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"http:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a><br>\n<\/p><\/div>"}  Click System Preferences...  Click Startup Disk  Unlock the menu. Click the original (grey) hard drive. Click Restart..., then click Restart when prompted. Open Finder and click the triangle-shaped "Eject" button to the right of your attached hard drive's name on the left side of the window. When prompted, you can physically detach the drive from your Mac.

Summary:
Restart your Mac. Press and hold ⌘ Command+R. Wait for the Apple logo to appear. Release ⌘ Command and R. Click Disk Utility. Click Continue. Select your other hard drive. Click Edit. Click Restore…. Click the "Restore from" drop-down box. Select your Mac's hard drive. Click Restore. Click Done when prompted. Close Disk Utility. Click Choose Startup Disk…. Select your original hard drive and click Restart. Open the Apple menu . Click System Preferences…. Click Startup Disk. Unlock the menu. Select your new hard drive. Click Restart…. Click Restart when prompted. Wait for your Mac to finish restarting. Switch back to the original hard drive. Eject your new hard drive.