Step 1: Download usb drivers for your device. Kies included this usb drivers. so you can install kies to your PC. Choose the correct Odin version to your device
Odin v1.83Galaxy S I9000, Galaxy S II I9000, Galaxy Giorgio Armani I9010, Google Nexus S I9020, Galaxy Note N7000, Google Nexus S, Galaxy Tab P1000, Galaxy SL I9003,
Step 2: Check your phone is fully charged, Press volume down button+ home button+power button Now your phone ask to press volume up button to continue to download mode.