Steam is an online service that lets you download computer games and play multiplayer games through the Steam Network. When you created your Steam account, you had to enter both an account name and password. Steam urged you to print the password out once your account was created. If you did not, you can still access your Steam account by resetting your password. While you can't technically "Find" your old password, you can use Steam's password recovery service to create a new one.
Launch the Steam client from either the desktop or "Programs." Click the grey "Retrieve Lost Account" button.
Click the circle next to "I know my account name," if you have your account name. If you do not, choose "I do not know my account name." Enter the email address associated with your Steam account. Steam will send you an e-mail containing your account name.
Click "Next" and type in your account name. Click "Next." Steam will display a "Working" message and then inform you that you have been sent an e-mail.
Log into your e-mail. Click the email from "email@example.com." Scroll down until you see a verification code consisting of different characters. Copy the verification code. Navigate back to the Steam client. Paste the verification code in the "Verification code" text box.
Enter the answer to your security question. You can find the question in the same e-mail as the verification code. Click "Next." Input a new password and click "Next." Write down the password so you don't forget it.
You must paste the verification code using "Ctrl" and "V." Right-clicking and selecting "Paste" will not work.