You need to have LAMP stack installed to set up Wordpress.
1) Install Apache HTTP Server
sudo apt-get install apache2
2) Check if its working by going to http://localhost/
3) Install PHP
sudo apt-get install php5 libapache2-mod-php5
4) In order for PHP to work with Apache you need to restart
sudo /etc/init.d/apache2 restart
5) Install MySQL
sudo apt-get install mysql-server
6) Optional Install phpMyAdmin (Recommended : Make's Life Easier)
sudo apt-get install libapache2-mod-auth-mysql php5-mysql phpmyadmin
7) To add phpMyAdmin to Apache web server you need to edit apache2.conf file
gksudo gedit /etc/apache2/apache2.conf
8) Add this to the last line of apache2.conf file
Include /etc/phpmyadmin/apache.conf
9) Then you need to reconfigure your phpMyAdmin package
sudo dpkg-reconfigure -plow phpmyadmin
10) Restart Apache and everything should work
sudo /etc/init.d/apache2 reload
Note: When you reconfigure phpMyAdmin it might ask about which socket you're going to use select Unix Socket.
The htdocs directory in Ubuntu is /var/www
apt-get install wordpress
? Then read the instructions in /usr/share/doc/wordpress