For client app, you connect to your AP, like you do with laptop, mobile phone, tablet.
So you have access to internet.
Then you connect to some address, eg google.com on port 80. And then using HTTP commands request page. You can use GET or POST command to get web page. Or you can post data to PHP script, using that two methods.
Here is some HTTP examples http://www.jmarshall.com/easy/http/
Other way is to use EMAIL, you connect to SMTP server to send email. You connect to port 25 of your server, eg smtp.yahoo.com port 25, and then log in using BASE 64 protocol for password, and send email.
https://www.cs.cf.ac.uk/Dave/PERL/node175.html
You can use putty to learn how to handle communication with server.

If you are using module in AP mode, you connect to module with your tablet, or other device, and then create web page in pic, and than display it on your tablet.
To do this, PIC must handle basic HTTP protocol. This is like setup page on router or AP.

All this protocol are text based, so if you are familiar with using UART and parse string, this wouldn't be to hart to master. It isn't too hard. There is example with different module:
http://www.picbasic.co.uk/forum/show...8906#post88906
http://mackrackit.com/mac/ichip/ichip.html
It's similar to GSM modem it isn't complicated as it might look.