I installed  Phalcon on Ubuntu 13.10 from  Official manual and faced some problems may make beginner confused.

I.  install Phalcon 

First of all. I installed php development resources & GCC compiler:
sudo apt-get install php5-dev php5-mysql gcc
Download & install phalcon:

git clone --depth=1 git://github.com/phalcon/cphalcon.git
cd cphalcon/build
sudo ./install
Faced first error:
/usr/include/php5/ext/pcre/php_pcre.h:29:18: fatal error: pcre.h: No such file or directory #include "pcre.h" ^ compilation terminated. make: *** [phalcon.lo] Error 1 
After checking for a while, Phalcon need : libpcre3-dev pakage :
apt-get install libpcre3-dev
wee need add new config in additional .ini files/

Create phalcon.ini file in /etc/php5/apache2/conf.d/phalcon.ini add : extension=phalcon.so in this file. 

Reload your server. It works !

II. Install Phalcon developer tool 

After installing Phalcon and Phalcon developer tool successfully . We may got new message when try to use Phalcon developer tool by phalcon command
$ phalcon
ERROR: Phalcon extension isn't installed, follow these instructions to install it: http://docs.phalconphp.com/en/latest/reference/install.html

It means your php cli didn't realase phalcon framework (phalcon.so). Wee need to add phalcon.ini files in configuration file of PHP5 cli. First of all, find Configuration file Path by command
 php -i | grep "Configuration File"

Configuration File (php.ini) Path => /etc/php5/cli
Loaded Configuration File => /etc/php5/cli/php.ini

#cd to Configuration Path
$ cd /etc/php5/cli/
$ /etc/php5/cli$ ls

conf.d  php.ini
You can see that we have another php.ini file and conf.d folder in Configuration path. Add phalcon.ini which contain extension=phalcon.so into conf.d folder.

Try your  phalcon command again . It works !