find wifi device

$ /sbin/iw dev
phy#0
    Interface wls3
        ifindex 3
        wdev 0x1
        addr xx:xx:xx:xx:xx:xx
        ssid xxxxxxx
        type managed
        channel 36 (5180 MHz), width: 20 MHz (no HT), center1: 5180 MHz
        txpower 15.00 dBm

scan for available N/W

$ /sbin/iwlist scan

for WPA2

install related packages

$ sudo apt install wpasupplicant

generate psk for a ssid

$ wpa_passphrase myssid
# reading passphrase from stdin
mypassphrase < input from stdin
network={
    ssid="myssid"
    #psk="mypassphrase"
    psk=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
}

add these lines to /etc/network/interface

auto wls3
iface wls3 inet dhcp
  wpa-ap-scan 1
  wpa-scan-ssid 1
  wpa-ssid myssid
  wpa-psk xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

change permission /etc/network/interface

$ chmod 600 /etc/network/interface