It's just notices, not errors. Notices are emitted when code violates what some people regard as good programming practices. There is no need to care about them unless you know PHP well enough to decide for yourself whether you want to follow those practices. (I have to point out, however, that it was notices who alerted me to a grave error in my code recently.)

If you don't want notices to appear, you need to change the warning level in your php.ini. The file is thoroughly commented and should be no problem to edit.