how to sync videos from PC hard disk to iPhone with itunes?
I assume you have the video's you want to sync to your iPhone allready in iTunes. When not, you can drag the video's into itunes.

Connect you device with the lightning/30-pins cable to your pc and open iTunes if it doesn't pop up automatically.


At the upper left corner there should be a small iPhone/iPad icon. Click on the icon to view more information about it.
In the left panel is a menu called video (or something like that)
check the checkbox that you want to sync video's with your device. When the video's are correctly loaded into iTunes they should popup here.
select the video('s) you want to have on your device.
in the lower right corner click on apply/sync (if i'm right) 


This will start syncing the video's from iTunes to your device.

When i'm right the video's can be found in the app called "video's".