How do I format an external HD to use with my ipad

APFS and HFS+ are Apple proprietary formats - not natively supported by Microsoft on PC. Similarly, NTFS is MS Proprietary- not supported by Apple. It is for this reason that the bast majority of non-platform specific third-party drives are formatted from manufacture as FAT32 or exFAT, these formats being generally universal.

Unfortunately, iPadOS does not provide tools to format or partition external drives. As such, you have to use an different computer, such as PC or Mac, to partition and format external drives.

IPadOS 13 supports Ex-FAT, FAT-32, HSF+, and APFS formats so if you have a Windows PC, format it as FAT-32 (it probably shipped formatted as Windows NTFS, which is not supported)

Nope. There are utilities for NTFS for MacOS (oldest likely is NTFS for Mac by Paragon Software, which I have and works very well). But there are no utilities for APFS or HFS+ for Windows.