I don't understand this code

I'm studying about the controller of the active suspension system, i follow the control tutorial for Matlab: http://ctms.engin.umich.edu/CTMS/index.php?example=Suspension&section=ControlPID but i don't understand this code

sys_cl=F*feedback(F*G1,C);

And this is a block system:

I don't understand that why we have the transfer function of close loop system with feed back like that (i mean this code), can some one explain it clearly? thanks so much.