How to sew a dress like this..plz help!!!?

This is most definitely not a beginner dress. Both the nearly strapless bodice (which will need considerable boning to look right) and the choice of fabric (chiffon) mean that it's highly unlikely you'll be able to make this unless you're very, very determined and you've got a good teacher working with you the entire project. Come back in about 3 years after you've learned to sew and revisit the idea of making this dress.