Need understanding

I'm trying to have my first child...I go by the apps eve too and don't get my results I really want...I bought my first ovulation test and I want to know how to use it ik the basic but I need to know when the right time to use it... I'm regular my period come every month...I did have moment when I was irregular but that when I was living with different females...I read if you regular your cycle is 28 days...count from you last cycle to your next expected period I counted pass 28 days...so please help me....