Edit /etc/apt/sources.list.d/zabbix.list and paste the following lines (for 2.2)
deb http://repo.zabbix.com/zabbix/2.2/debian/ wheezy main contrib non-free deb-src http://repo.zabbix.com/zabbix/2.2/debian/ wheezy main contrib non-free
or (for 2.4)
deb http://repo.zabbix.com/zabbix/2.2/debian/ wheezy main contrib non-free deb-src http://repo.zabbix.com/zabbix/2.2/debian/ wheezy main contrib non-free
Then add the gpg key
gpg --keyserver keys.gnupg.net --recv D13D58E479EA5ED4 gpg --export --armor D13D58E479EA5ED4 | sudo apt-key add -
and update the apt package list with
apt-get update
Install the Zabbix agent
apt-get install zabbix-agent
and edit /etc/zabbix/zabbix_agentd.conf to configure it. In a simple passive-agent configuration you have at least to set the server address
Server=my.server.address
Finally, restart the agent to reload configuration with
service zabbix-agent restart