If you are having issues with WiFi and have OS X 10.11.2 El Capitan, then you will need to upgrade to OS X 10.11.3 or later. On your notebook, go to Apple | App Store | Updates; then update your current version of Apple OS X El Capitan. Make sure to back up your data just in case.

NOTE: Not sure you know what version? In the upper right corner of your desktop, click on the "Apple" icon and select "About this Mac."