Have 300 users signed up on Facebook. What Next?

So I built a viral website that's picking up momentum.
I added a Facebook Login button on my website and noticed that it has generated about 300 signups. Now, I have the details of about 300 users - their personal email and Facebook name, URL etc.

I'm a noob at Facebook App and don't fully understand how that works.

• Is there a way I can use this data to retarget these visitors?
• What else can I do with this kind of data?

Thanks!