zabbix_agent don't start

[dividedby0]

hi Everybody

I'm new in Zabbix.
I followed the installation guide to install zabbix_server and zabbix_agent on the same machine.
I created an item which key is icmpping.
I also created a trigger which expression is {localhost:icmpping.last(120)}<1.

But when I start monitoring, I get nothing.
Indeed when I lauched ps-aux |grep zabbix_agent I got nothing.

My install doesn' create zabbix_suckerd and trapperd either.

So If someone can Help me,

THanks a lot
Regards

Rose