If you don't want to touch the interface of a terminal, just search for a partitioning program. On most Linux Distributions a graphical one comes pre-installed. If you can't find one, install GParted, I can highly recommend it. Else, yes
cfdisk should be the way to go.
On Windows you can also find good software, just search for a partitioning program.
You need to select the device. And reformat it, by creating a new partition table. (To you I recommend MS-DOS even though
gpt is better.) On each disk, there is a partition table, that indicates where on the disk the partitions are. Partitions are just spaces with which software, including operating systems, can interact. Software can not interact with the device in form of read/write, it does this with partitions.
Than choose the new filesystem for the disk wide partition. (The most compatible one is
fat32. If you want to install an operating system, it formats the partition to the filesystem it needs, during the installation.) Creating multiple partitions is the logical dividing of the disk into multiple spaces (like you have multiple disks to write to).
If after creating a new partition table the entire device still gets shown as only 34 GB, then on that 3TB device is a virtual device that has a volume of 34GB, and every time you format it or create a partition table, you are just interacting with that virtual device. Had the problem myself with a USB.
Hope this was helpful. If so, I appreciate an answer acceptance. (Just trying to get 50rep so I can god damn finally comment on stuff.)