To install Windows 10 on a custom partition, use these steps:

1. Start your PC using a Windows 10 USB flash media.

1. 1. Press any key to begin.
   2. Click the Next button.
   3. Click the Install now button.
      

      

   4. Type the product key, or click the Skip button if you’re reinstalling Windows 10.
      

      

   5. Check the I accept the license terms option.
   6. Click the Next button.
   7. If you skipped the product key, select the edition of Windows 10 that you’re about to install.
      

      

   8. Click the Next button.
   9. Select the Custom: Install Windows only (advanced) option.
      

      

   10. Select each partition in the hard drive to install Windows 10 and click the Delete button. (Usually, the “Drive 0” is the drive that contains all the installation files.)
       Warning: Deleting a partition also deletes all data within.
   11. Select the Drive 0 Unallocated Space.
   12. Click the New button.
       

       

   13. 

   14. Click the Apply button.
   15. Click the OK button. (Alongside the custom partition, Windows 10 will also create the additional partitions automatically required to install and run the operating system.)
   16. (Optional) Select the Drive 0 Unallocated Space.
2. Click the New button to create additional partitions with the remaining space. (You can always perform after the installation.)
3. Select the Drive 0 Partition 4 (Primary) from the list.
4. Click the Next button.
   

   

Once you complete the steps, the setup will install Windows 10 on the custom partition you created. After the installation, you will need to go through the out-of-box experience (OOBE) to create an account and finish configuring the installation.