Libremesh Wifi help

I am trying to use Libremesh firmware on 3 Gl.inet ar300m devices, and I am really happy for my mesh-net, very easy to configure.
I would like someone to help me to set un a wifi client connection: everything works if i connect one devide via ethernet cable to internet (through another router/modem), but I am not able to give to the mesh-net the internet connection via wifi: I think I should create a new wifi connection and a new item in interfaces page. Can anyone help suggesting step by step?

Thank you so much!!