Floral Satin Ribbon What Do I Wear To A Wedding?

What do I wear to a wedding? - floral satin ribbon

My friend is 23 year old cousin wedding in June What should I bring? I have a satin floral dress is a sort of Nice, I wore my graduation from college, but my sister told me that there should be better than the bride. He is white, red and black. Okay? What do girls usually wear to a wedding /