What is Odin ? latest Odin is a software for Windows which with the new Android firmware files you can install on a Samsung Android phone with use the odin program. So you can Flash a new ROM (firmware). Odin v3.07 is available free of charge. so you don't need to pay it
It is rumored that it comes directly from Samsung and it also uses Samsung. Odin is a good alternative to Samsung Kies.

This is the Screenshot of ODIN

Read also : root and install cwm on galaxy s3

With Kies, you get only the updates that previously have been adjusted by the operator. These adjustments take mostly forever or there is no only. You can install any available official or unofficial firmware with Odin. You have to watch always carefully installed the correct ROM to the appropriate Samsung phone.
Is the Samsung phone in download mode it can go. With the download reset repair plug can put his phone in download mode.
Below is simple way to use odin

1. ODIN
2. Firmware / Rom that you want to use. you can find here download galaxy s3 firmware
3. USB connector
4. and make sure your galaxy s3 battery is an full state or more than half.
5. for more complete tutorial how to flash galaxy s3 with ODIN you can read here : flash galaxy s3 via odin

Download Odin v3.07 Here are the download links latest Odin v3.07