--> In this example configuration wireless is wlp0s20u7, you must change it to your personal address.
You must also substitute to WIRELESS your SSID and to password your WiFi password

A) INTERFACE NAME

Find the interface name:
[audiolinux@archlinux ~]$ ip addr show

...3: wlp0s20u7: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 00:1f:33:fe:fc:05 brd ff:ff:ff:ff:ff:ff

Set interface UP:
[root@archlinux audiolinux]# ip link set dev wlp0s20u7 up

B) WPA SUPPLICANT CONFIGURATION

Install wpa supplicant:
pacman -S wpa_supplicant

Create the wpa supplicant configuration file:
[root@archlinux audiolinux]# touch /etc/wpa_supplicant/wpa_supplicant-wlp0s20u7.conf

Edit the new file adding the content below:
[root@archlinux audiolinux]# nano /etc/wpa_supplicant/wpa_supplicant-wlp0s20u7.conf

ctrl_interface=/run/wpa_supplicant
update_config=1


Start wpa supplicant:
[root@archlinux audiolinux]#  wpa_supplicant -B -i wlp0s20u7 -c /etc/wpa_supplicant/wpa_supplicant-wlp0s20u7.conf
Successfully initialized wpa_supplicant

--> if iw is not installed, install it first with:
pacman -S iw

Note: we are using iw because the scan funcion in wpa_cli (see below) is not always working

Let's find if your SSID is recognized:
[root@archlinux audiolinux]# iw dev wlp0s20u7 scan
...
SSID: WIRELESS
...

In this case the name is WIRELESS

Now we start the wpa command line interactive interface:
[root@archlinux audiolinux]# wpa_cli
wpa_cli v2.6
Copyright (c) 2004-2016, Jouni Malinen <j@w1.fi> and contributors

This software may be distributed under the terms of the BSD license.
See README for more details.

Selected interface 'wlp0s20u7'

Interactive mode

> add_network
0
> set_network 0 ssid "WIRELESS"
OK
> set_network 0 psk "password"            
OK
> save
OK
> quit


Now check configuration file with:
[root@archlinux audiolinux]# nano /etc/wpa_supplicant/wpa_supplicant-wlp0s20u7.conf
It should have this inside:

ctrl_interface=/run/wpa_supplicant
update_config=1

network={
    ssid="WIRELESS"
    psk="password"
}


--> Eventually remove disabled=1

Enable wpa supplicant at boot with
[root@archlinux audiolinux]# systemctl enable wpa_supplicant@wlp0s20u7
Created symlink /etc/systemd/system/multi-user.target.wants/wpa_supplicant@wlp0s20u7.service → /usr/lib/systemd/system/wpa_supplicant@.service.

C) SYSTEMD NETWORK CONFIGURATION

Create the systemd network configuration file:
[root@archlinux audiolinux]# touch /etc/systemd/network/wl.network
Edit the new file adding the content below:
[root@archlinux audiolinux]# nano /etc/systemd/network/wl.network

[Match]
Name=wlp0s20u7

[Network]
DHCP=yes

--> If you will use only wireless, remove all the other entries in /etc/systemd/network

D) REBOOT AND CHECK

Reboot the system:
[root@archlinux audiolinux]# sudo reboot

After reboot, check your network. You should see something like this:

[audiolinux@archlinux ~]$ networkctl
IDX LINK             TYPE               OPERATIONAL SETUP    
  1 lo                    loopback           carrier             unmanaged
  2 enp3s0            ether                 routable          configured
  3 wlp0s20u7       wlan                 routable          configured

...and remember to choose Save from Menu if you are in RAM mode