I am pretty new to this and I am trying to boot Ubuntu from a 1Tb extra hard drive. I have the iso installed already but not sure where to go from there. I've read about burning it to the external drive, which isn't working out out for me. I've also seen some posts about partitioning but I'm not sure what that means.
Do you want a regular installed Ubuntu system in this target '1Tb extra' hard drive? Or do you want a persistent live system? Both are possible. See this link and links from it,
Backup whatever data are stored in the 1Tb extra hard drive to another drive or to the 'internet cloud'.
Installed system (more stable, fairly portable)
Create a USB boot pendrive with a cloning tool, for example
Boot from the USB boot pendrive drive and install Ubuntu to the target 1Tb extra hard drive.
It will be easier and safer if you remove the internal drive before installing to the 1Tb extra hard drive. Otherwise, in UEFI mode, the bootloader will be installed into the internal drive. If it is impossible to remove the internal drive in this target computer, you can create the USB boot drive in another computer. Avoid proprietary drivers! Move the drive to the target computer, and if necessary, install proprieatry drivers (typically for graphics and wifi).
Persistent live system (more portable, fairly stable)