For Ubuntu 16.04 LTS:

$ wget http://repo.zabbix.com/zabbix/3.0/ubuntu/pool/main/z/zabbix-release/zabbix-release_3.0-1+xenial_all.deb
$ sudo dpkg -i zabbix-release_3.0-1+xenial_all.deb
$ sudo apt update

For Ubuntu 14.04 LTS:

$ wget http://repo.zabbix.com/zabbix/3.0/ubuntu/pool/main/z/zabbix-release/zabbix-release_3.0-1+trusty_all.deb
$ sudo dpkg -i zabbix-release_3.0-1+trusty_all.deb
$ sudo apt-get update

Install Zabbix Agent

$ sudo apt-get install zabbix-agent

Edit Zabbix Agent Configuration

 $ sudo nano /etc/zabbix/zabbix_agentd.conf

After adding zabbix server ip in configuration file, now restart agent service using below command.

# /etc/init.d/zabbix-agent restart

To start and stop zabbix-agent service anytime use following commands.

# /etc/init.d/zabbix-agent start
# /etc/init.d/zabbix-agent stop