"From now on" means "starting now and continuing in the future". You use this to talk about doing something differently than before:
I think I paid too much. I'm definitely going to shop around for a better price when I buy a car from now on.
When you tell someone else what to do "from now on", it sounds a little angry or stern. You can speak this way to your employees, your family members, or someone who you have authority over:
From now on, I want you to call me if you're going to be out past ten o'clock. Do you understand me?
From now on, can you check with me before you do something like that?
A softer-sounding (and more formal) phrase for work situations is "going forward":
Some English learners use the expression "from now", but that's incorrect.