If you already know how to program learning php will be simple. It was my 20th language and it took me like a week to pick it up, though I am always learning new tricks with it.
If you do not already know how to program, learn that first. Learn the theories and methodologies behind programming then learn php. I don't recommend php as a first language cause it is a special purpose language and you're better off to learn a general purpose language (like C or Java) first.