GNU/Linux Debian Stretch Installing Broadcom BCM4311 Driver Guide
Hi! The linked Tutorial shows you Step-by-Step How to Install Broadcom BCM4311 Wi-fi/Bluetooth Driver in Debian Stretch 9 GNU/Linux.
The Package Provides the Source Code for the wl Kernel Modules and makes use of the DKMS Build Utility to Install them for the Running Kernel.
GNU/Linux Debian 9 Broadcom BCM4311 Driver Installation Guide
BCM4311 Driver Debian Stretch Installation Guide