To lock your Samsung Galaxy S GT-I9000 phone screen with a password, you can adopt the following steps.
Step 1: Open Settings.
Step 2: Access Location and security.
Step 3: Choose Set screen lock.
Step 4: Select Password.
Step 5: Enter a password containing at least 4 characters and tap Continue.
BTW, the password can consist of numbers, symbols and letters. Moreover, it must contain at least 1 letter.
Reference Articles:
Android USB Driver for Samsung
How to Set Password on Samsung Galaxy S3 I9300/I9308
How to Set Password on Galaxy S4 GT-I9500/GT-I9508
How to Open USB Debugging in Samsung Galaxy S5
