Hello,
Question is in the title, could someone help, I am little newbie in IC 
Thanks
That depends on your check.
If your check produces a state change in icinga service then icinga2 can send a notification if configured properly.
ok that’s what i ld like to do, how to set up the .conf file to set up >green % >yellow >80% >red90% + send alert by mail ?
After setting the thresholds for your check in your service you need to attach a notification object that uses user and/or user group objects.
How to define and attach those objects is documented here:
https://icinga.com/docs/icinga-2/latest/doc/03-monitoring-basics/#notifications