from the url: http://www.mikesimonds.com/getting-started-php-salesforce-t117.html Credit goes to this site and this developer for being awesome.
Peter thanks for joining the site and I hope that I can help you, so let's give it a try:
1) You can use PHP with salesforce to perform almost any action you want with your projects. We currently use PHP to update, insert, and upset(salesforce function) to update all our data in salesforce for accounts, products, pricebooks and custom objects within salesforce. You can use PHP to create data or populate data from an object to a custom object using outbound messaging. You can use PHP to create a complete replication process of your data in Salesforce to a local database such as MySQL or Oracle. We do all these types of functions using PHP.
You will not be able to or would want to store your php scripts on a Salesforce server, they will all reside on your personal server or a company server. We have two servers, one for production and one for development that run Apache, PHP, and MySQL. The PHPToolkit is basically a group of scripts that are a class that is used to communicate with Salesforce's API.
The best way to get started is, and I am assuming that you have a windows PC, to download a free WAMP(windows apache web server for localhost development) and install it on your PC. You can do all the development on your local pc, that is what I do. I use XAMPP and since you are from Germany, here is the link > apache friends - xampp
Once you get that installed, follow the link from my main menu to the PHPToolKit and download it. There are some instructions and examples in the folder system within the zip file that will help you get started. I will also be glad to help you offline get setup
2) Once you have a webserver or localhost installed and have the toolkit installed, you can connect to Salesforce's API using your administrator Salesforce Account. If you want to have a development Salesforce account, which I would suggest, you can sign up for one for FREE > Force.com Developer Edition Sign-Up
The WSDL file can be downloaded right from wihin your Salesforce Account. Once you login to Salesforce, go to Setup > App Setup > Develop > API and you can generate a Partner WSDL file from there and then add that to your localhost or webserver and you can start development
I hope some of this makes sense, It seems like a lot, but it is not really. Let me know if you need any clarification and catch me on Skype anytime