Generally, if you just listen to the music and the rhythm of the song, you would know when it is the right time to hit the notes. That being said, I think it's too early for you to be using mods. Just play nomod for now and gain some experience.
You should practice on difficulty you usually play nomod. Listen closely to the music and feel the song, that's the best way to hit circles. And of course get used to it
If you dont know when to hit with HD, your rhythm sense is shit and you should not play HD until you learn "how to osu".
"Overall, I think people tend to reveal their true selves when they step into an avatar. As I said earlier, they probably feel some sense of freedom. But freedom easily gained quickly turns into a false sense of omnipotence."