I'm posting these 2 video to show how to use Odin3 to the persons that never used it:
1. For S6 and previous models:
2. For S7 and successive models:
It is pretty simple, you just have to put the phone in download mode, then connect it to the PC with the USB cable, the first time you will see that Windows will install the phone drivers, it will take 2 minutes, once done you just have to select the unzipped rom (or the rooted kernel or whatever you need to flash), then push START, the flashing procedure will start and you will see a progress bar on the phone screen.
The S6 video shows you to get the roms from http://www.sammobile.com/firmwares/
by the way that site is slow, we suggest you to use our repository instead: https://idoneapps.com/forum/index.php?topic=8.0
On the S7 video it is suggested to have Smart Switch software because it automatically installs all the required drivers for the phone, you can get it here:http://www.samsung.com/us/smart-switch/