Is Realm Works for me?

[H2Os]

So Realm Works sounds great, but I've a few questions and concerns.

Is Realm Works primarily for online campaigns? If not and is indeed intended for actual table top play, then everyone in the group would need to have a computer/handheld device?

I'm currently running a group through Rise of the Runelords. Does Realm works function for campaigns that are already built? Or is it primarily for GMs creating their own world?

Thank you for your time.

H2Os