Step by Step Instructions on Resetting your Nexus S
1. Start with the Home Screen by tapping the last button in the lower righthand corner (the house icon).
2. Tap the Menu button (second from the left) and select Settings.
3. From the Settings menu, select Privacy.
4. Step 3 will bring you to the Privacy Settings menu. Under the "Personal Data" tab, select "Factory data reset."
5. On the "Factory data reset" screen, there is a message reminding you that this action is irreversible. So long as you agree, tap the checkbox to the left of "Erase USB storage" and then tap "Reset phone."
6. If you have an unlock pattern setup, you will be asked to verify it. After which, you will be reminded yet again that this action is irreversible. Tap "Erase everything."
This last bit should take less than a minute. The phone will automatically restart, and you can start anew, sell the phone, disassemble it, etc.