locking up and freezing challenge re-booting

question answered that it is probably the Hard drive and suggestion is to boot from external usb drive.

Confused how this will work w/o OS on the external drive?

Also how will I get the osx back with all of the recovery partition on the new drive?

Will time machine have all of the info needed ?

Followed the answer on the original problem.

received an update to Sierra, now the computer is acting normal w/o any lockups.

The second question is where I needed to think about replacing the original drive.

Time Machine, I understand does not clone the original drive therefore what are the steps to set up a new drive or re-formatted drive to get the recovery partition on the new drive? Does it go back to Lion OS X? why would I need to re-install the original OS X?