Spanish slang

This post could appropriately be titled as: "Angela's version of the different Spanish slang she's picked up on."

I don't quite yet know how to apply the different slang words and gestures I've picked up on, but I thought I'd share some of the different things I've noticed. *Warning: these definitions are just what I think the phrases mean. I could be really wrong.*

• Qué guay: equivalent to "how great," "wow," "wonderful," "qué bien"
• Vale: pretty well known, meaning, "okay," "great," some form of acknowledgment that you agree or that you understand
• Madre mia: (pronounced: moooahdre mia) literally speaking, "my mom," but from what I can tell, it kind of means "oh my goodness," "oh, wow," "oh my gosh." But the intonation is KEY. You start low, go up, and then go down, and go back up again but not as much as when you did while saying "-dre"
• Está leche: still quite not sure what this one means. I think it suggests, "___ is awesome." But I could be wrong.
• Vamos a ver: I guess it's not really slang, but I find myself saying it really often. "Let's see," or "let's wait and see" is the best translation I've got.
• The last one is more of a gesture. I don't know what it signifies, but even my professors use it. I've included a video of demonstration. I'm up for suggestions on what this hand gesture could mean.

I know it's a little silly, but I'm serious, they make this hand gesture in daily conversation and even during lecture. (I feel slightly bashful of putting the video up, and it kind of makes me want to burst out laughing every time I watch it.) I've altered the speed of the hand motion to suggest that I've seen various versions of this hand slang. LOL What could this mean?

;P