Format Drive for Time Machine

One should not use a drive for both Time Machine and normal file storage. If the drive should fail the partition for normally storage will be lost as that would be the only copy of those files.

The format for the TM drive should be OS X Extended (journaled) with a GUID Partition Map.

You can make one, two, or. more partitions - that is up to you. That has nothing to do with formattingexcept that it will format while partitioning. It is your decision. do make it mac OS extended (journaled). If you have more than one partition, you can use one for Time Machine and the other for other backups, however, it is not good to have all your backups on one drive - if that fails you will lose them all.

You don't know how the drive was formatted, so formatting it would be a good idea.

Drive Partition and Format - El Capitan or Later

1. Open Disk Utility in the Utilities' folder.
2. After Disk Utility loads select the drive (out-dented entry with the mfgr.'s ID and size) from the side list. 
3. Click on the Erase tab in the Disk Utility toolbar. A panel should drop down.
4. In the drop down panel set the partition scheme to GUID. Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
5. Click on the Apply button and click on the Done button when it is activated.
6. Quit Disk Utility.

You wil find that the above will prove difficult if the drive was pre-formatted for Windows.