Tag Notification is allocated for generating Alarm notification whenever a Tag is above or below the limit. 

You should have to select Group which you want to send Notification and you should have to select Device and then select your Tag. 

When you Configure a Tag in Tag Configuration which is done at the time of Device Configuration,  at that time you should have to config that particular tag value is assign in HI,HIHI,LO,LOLO range . 

When that particular tag value reach that HI, HIHI, LO,LOLO range value then it will generate Tag Notification. 

Please Fill up all required field and click on save button.