The flowery symbol is Prof. Delcamp's way of indicating that the previously played open string must be stopped at the same time as sounding the note with the flower symbol. Stopping strings is an entire subject unto itself, and should be learned early. There are several ways of stopping a string with the right hand, and several ways with the left hand.
Until someone more experienced than I jumps in, it sounds to me that you need to raise the metacarpophalangeal joint of your fourth finger to be the same distance from the edge of the fretboard as the other metacarpophalangeal joints, so that you will have more control over the use of the fourth finger. It should be perpendicular to the fret board, otherwise it will be too weak and difficult to control.
Yisrael van Handel
Modi'in Ilit, Israel