Q: I am having to use the guest user due to me forgetting my password. Do you know how to find out my password?

Resetting or changing a password:

For Snow Leopard or earlier:  http://support.apple.com/kb/HT1274

For Lion or later:  http://support.apple.com/kb/HT6022

If the user account is associated with an Apple ID, and you know the Apple ID password, then maybe the Apple ID can be used to reset your user account password.

Otherwise*, boot into Recovery mode. When the OS X Utilities screen appears, select

Utilities ▹ Terminal

from the menu bar. In the window that opens, type this:

res

Press the tab key. The partial command you typed will automatically be completed to this:

resetpassword

Press return. A Reset Password window opens. Close the Terminal window to get it out of the way.

Select your boot volume ("Macintosh HD," unless you gave it a different name) if not already selected.

Select your username from the menu labeled Select the user account if not already selected.

Follow the prompts to reset the password. It's safest to choose a password that includes only the characters a-z, A-Z, and 0-9.

Select

 ▹ Restart

from the menu bar.

You should now be able to log in with the new password, but your Keychain will be reset (empty.) If you've forgotten the Keychain password (which is ordinarily the same as your login password), there's no way to recover it.

*Note: If you've activated FileVault, this procedure doesn't apply. Follow instead these instructions.