mask out the stems and leaves with the liquid. when the masking fluid is dry, then you can paint the background without worrying about getting any of the paint in the flowers.
there are a few tricks to using the masking fluid. first of all, use an old brush because some masking fluid is very difficult to remove from the bristles. i have ruined several brushes over the years with masking fluid. secondly, rub the brush bristles in soap before dipping in the masking fluid. the soap will make it easier to remove the masking fluid from the brush. be sure to wash your brush immediately after finishing with the masking 