I want to develop web based control software for the Pi in PHP. I have some experience in PHP , but i have experience in using PHP, but no experience in running it on a Raspberry Pi.
You can start off by setting up a simple apache server you can then use PHP for something like creating a dashboard that displays data from the sensors you connect to your Pi. I made a similar project for a high school hackathon last year.
Some tutorials to help you get started:
I assume you mean to ask: what do I need to make gpios and other pi-specific stuff usable in PHP?
I would encourage in using some other tech, but if that's your choice my gut feeling would be to just have some
system calls, see this example.
The performance won't be exciting but it's acceptable for watering the pots or turning on a lamp.
A quick google of PHP libraries for GPIOs resulted in multiple matches, I wouldn't feel like using any but you can take the chance to experiment with them.