says, you need the Window list in your panel.
The different versions/desktops of Mint all use different ways of doing this.
If using Mate - follow the above instructions.
If using Cinnamon:
Go to Cinnamon Settings > Applets > tick box "Cinnamon Window List"
xfce and KDE each have their own method also.
@takis13 - welcome to the forums to you as well