DRoidWall is basically a firewall. In a nut shell, you can block apps from accessing your wifi or mobile data (for limiting things like warez or non-internet based apps from using your data or getting advertisements) Eh, at least thats what is possible.
this has happened to me randomly but only on first install it blocks everything, then I have to white list things. Confirm your white lists, you can always unlist it, then white list it again.
as with any issues, reboot helps things.