HELP! I want to install windows 10 from usb drive HELP!

[GTX155]

I'm building PC for first time and i need to make no mistakes.
When i install it does it need the usb drive to be plugged in to operate or it installed forever on the HDD how i want to be.
And how much space it will take on my usb is 8gb enough.

 

[bxflow]

The USB only needs to be plugged in for the installation, you can unplug it after as the OS will be installed on your HDD anyways. 8gb should be more than enough.

 

[BringerOfTea]

to create the bootable usbdrive i believe it took about 3,9 gb.