How can I know or tell if I am actually in a state of grace or not???
You are in the state of grace if you are baptized and are free from mortal sin.
We can have moral certainty not absolute certainty. If you have confessed your mortal sins you are in a state of grace (but you leave it with any new mortal sins). If you’re not sure if your sins are mortal, you can still go and confess them and maybe talk to the priest how to tell the difference. You can still confess venial sins too
A quote from St. Francis de Sales said that one helpful way of having some indication of being in a state of grace is if we’re not willing to offend God in the slightest.
Make a good Examination of Conscience and Confess regularly, perhaps once a month. Go to Mass and pray regularly.