what exactly is meant by web services for mobile apps? and how can they be created easily?

We have a classified ads website at strulia.com. We recently tried to hire a developer to develop a mobile app that would complement the website with the same features as the website. He said we need to create the web services(like its something huge). What is this? We told hime we had the MySQL database and XML feed that you could connect with php or something similar. but he insisted with this web services being developed separately. What am I missing to undertand? I have no experience in java or objective-c. If not enoough with some php connector, then how do we create this "web services" for our website and db to be ready to communicate with mobile apps?