This page is going to express how to connect your mobile device.
Recent Android phones
Plug your phone to your computer using a USB cable adapted for your device. Make sure this USB cable has a data line (not all cables do).
On your smartphone, you should see the charging icon. If this is the case, go to your notifications, scroll to the bottom until you see the notification saying that your phone is connected in "Charging mode".
Click on the notification, and then set it to "File transfer mode", "MTP" or something similar.
You should now see your phone being detected by most desktop environments.