You just have to tap whenever the inner colored circle is close to the outer ring.
Simply slide along the line through the small circles. You don't need to wait for the scanline, but if you drag too far ahead you might mess up your rhythm.
A drag note that starts with a tap. Tap the head note and slide along the line through the small circles.
Have your finger on the circle before the scanline has reached it. Hold it there until the scanline has gone to the end of the line coming out of the circle. You don't need to release it. You also don't need to tap it like the click note, so you can slide onto it like a drag note.
A variant of the hold note. You usually need to hold your finger for multiple pages. You can see how long you need to hold if you look at the pulsing ring around the circle.
A different version of click notes. You need to tap and slide away from it horizontally.