What Kim said!
If you want to use flock, you need to put down a good glue like KI Gloo. Sprinkle the flock over the top. I like to pat it in a little, but this will make your glue expand so you have to sort of figure out how much glue to use. Then I let it dry before tapping off the excess.
What you need to emboss is called embossing powder. There's lots of different brands. HTH!