First set your Wireless Interface to Monitor Mode using command :
airmon-ng start <interface>
Example :
airmon-ng start wlan0
To see what's your interface run iwconfig. If the output looks like this when run airmon-ng :
Run : airmong-ng check kill
After that run iwconfig to check if Monitor Mode Enabled
After everything goes well let's run airodump-ng to see available Wireless Network :
airodump-ng wlan0