Hey, Thomas if you know basic programming then you can learn PHP easily.
Always remember all programming languages require initial logic, What I mean is for programming it requires logic what ever may be the programming language is. We just learn the syntax and methods to write the logic.
For PHP, try the online manual at http://www.php.net/manual/en/
There is also offline version too, you can get it by searching on Google.
PHP manual is the best book/e-book for learning PHP. The manual contains good explanation of the code with well written examples.