Managed Mode: View/ Capture packets meant for source device only
Monitor Mode: View/ Capture all the packets that are present in an area

Disable Interface

# List Wireless Interfaces
iwconfig 
ifconfig <interface> down
 
# Kill Network Manager and processes listening on Interface
airmon-ng check kill 

Enable Monitor Mode

iwconfig <interface> mode monitor

If iwconfig command does not work for adapter or the adapter does not behave as expected use the following command

airmon-ng start wlan0

Enable Interface

service network-manager start
ifconfig wlan0 up