Here's how to automatically or manually back up your data, and then restore it on your Mac using Apple's Time Machine feature ...

Connect your Time Machine drive then launch Migration Assistant and select “From a Mac, Time Machine backup, or Startup disk” when asked where you want to import from.

You say you have the backups from two old MacBooks that you want to put on a single new iMac? Chris Breen shows the way.

You can restore your Mac using Time Machine and an external hard drive. Time Machine automatically creates backups of your Mac every hour.