I can not find the button for entering a file path in the "Files" file manager (GNOME Files). The current program menu does only offer the options "New Window" and "Quit", the other menu (in the taskbar) only shows my favorites and the default stuff that is shown for most programs. Also I can not find anything in the preferences.
See this question about Ubuntu 13.10.
The shortcut CRTL + L still works, but I can not find the "menu way".
The only way you can enter a specific folder location into GNOME Files (a.k.a. Nautilus) is by using the keyboard shortcut that you mentioned, Ctrl + L. There is no way you can do this only by clicking/via menus.
However, if you need this feature in your file manager, you can use Dolphin - the default file manager for KDE Plasma (Kubuntu). Dolphin allows you to enter specific folder locations by clicking the address bar at the top of the window.
See this question for installation instructions.
It is like you found out: typing Ctrl+L is the way to enter a path. There is no menu anymore, nor a clickable button.
Unfortunately, such GUI item doesn't seem to exist even as a nautilus extension.
You can, however, simplify it to one key press by simply pressing /.
If you want nautilus to permanently always show the path field by default, run this command in the terminal:
dconf write /org/gnome/nautilus/preferences/always-use-location-entry "true"
... and to disable that, run this:
dconf write /org/gnome/nautilus/preferences/always-use-location-entry "false"
