First you should enable ssh. A guide is found here:
1 Raspberry Pi
(connected to a router and the Internet)
When the webserver is installed you probably want to add files with ftp:
See step 2!
If you want to make the webserver visible on the Internet look here:
Step 1: Install Apache
If you havent set up ssh a guide can be found here:
Run the commands:
sudo apt-get update
sudo apt-get install apache2 php5 libapache2-mod-php5
Now your Raspberry Pi should display (if you open it in your browser):
If you are uncertain of address type ifconfig in your ssh-window. Should be 192.168.1.12 for example.