To create Windows 10 installer in USB Flash drive without additional tool/software:
1. Insert Windows 10 Disc installer to DVD drive, or if you use ISO image, please mount to be a drive.
2. Insert/connect 8GB USB Flash drive to the USB port.
3. Open the File Explorer to know the drive letters for DVD containing Windows installer and for the flash drive.
For example in My laptop, the drive letter for DVD installer is F, and for the USB Flash drive is H.
7. Type: select disk 1 then hit Enter.
There will be a note: disk 1 is now selected disk.
10. Type: Select partition 1 then hit Enter.
12. The next command is to format the flash drive.
14. To exit from diskpart type: exit then hit Enter.
See again the drive letters ( in this sample/mine, DVD drive is F, and the flash drive is H).