formatting USB with FAT32 or NTFS on MAC

Without third party software, you cannot format a drive as NTFS, or write to one.

Best choice would be ExFAT as FAT32 has a 2 GB file size limit.

Open Disk Utility. Choose the physical drive name of the USB drive in the column. Click the Erase button in the top row. Use these settings (using any name you want). Then click Erase.

You WILL lose anything currently on the drive. Copy anything off you need to save, first.

What are you planing to do with this external drive..?

Most off the shelf external drives already come formatted Master Boot Record / FAT32 or exFat.

If it is formatted something else like GUID Partition Map / APFS or Mac OS Extended (Journaled)..?

You need to select the whole external drive, then erase and format it back to Master Boot Record / FAT32.

Good work... 👍