Install Zabbix Agent

First, log into Zabbix agent instance and add the Zabbix repository with the following command:
Change version number for your zabbix version.

# wget http://repo.zabbix.com/zabbix/3.4/debian/pool/main/z/zabbix-release/zabbix-release_3.0-2+stretch_all.deb
# sudo dpkg -i zabbix-release_3.0-2+stretch_all.deb
# sudo apt-get update -y

Install the Zabbix agent by just running the following command:

# sudo apt-get install zabbix-agent -y

Once the Zabbix agent is installed, you will need to configure Zabbix agent to communicate with Zabbix server. You can do this by editing the Zabbix agent configuration file:

# sudo nano /etc/zabbix/zabbix_agentd.conf

Change the file as shown below:

    #Zabbix Server IP Address / Hostname

    Server=192.168.0.103

    #Zabbix Agent Hostname

    Hostname=zabbix-agent

Save and close the file when you are finished, then restart the Zabbix agent service and enable it to start on boot time with the following command:

# sudo systemctl restart zabbix-agent
# sudo systemctl enable zabbix-agent

Source: https://www.howtoforge.com/tutorial/install-zabbix-monitoring-server-and-agent-on-debian-9/