Disk encryption protects the data on a hard drive from being read by someone that isn't authorized. Disk encryption works by converting the information on the drive to unreadable data.

A disk encryption software is used to encrypt all the data on a disk. Once a disk is encrypted, then unauthorized personnel cannot access the data storage in the disk.

Firstly you require a program to do the encryption and ensure your system is compatible. Many programs are available that offer this capability and the steps would vary.

A trusted platform module (TPM) is a chip that handles FDE (full-disk encryption) and other encryption-based security on a computer. It is primarily used in operating systems such as Windows 7 and 8 with the advent of BitLocker, which if enabled will disallow you from using the hard disk in another computer.

That depends on encryption you are using. In any case OS creates partitions and formats it (or specialized software). Next if you have software encryption, than special driver is installed which either encrypted files or whole disk by intercepting read and write operations called by OS. If you have hardware encryption, then your whole hard drive is encrypted on hardware level. It means that hardware has extra steps before writing or reading information on hard drive.