I'm using Ubuntu 14.04 LTS a little while and I consider myself a beginner.
I am using the Nautilus file manager:
I wonder if you can navigate the folders through the directory tree, like in Windows through folders or the + sign.
Install Nemo file manager in Ubuntu (Unity)
Warning: do not use this PPA if you're using Linux Mint or if you use Cinnamon in Ubuntu! Also, if you've added any Cinnamon PPAs, remove them before using the WebUpd8 Nemo PPA even if you didn't install Cinnamon, or else the Nemo version in the WebUpd8 Nemo PPA might be overwritten.
Update: the PPA now provides Nemo 2.8 for Ubuntu 15.10, 15.04 and 14.04.
Add the PPA and install the latest Nemo with Unity tweaks/fixes by using the commands below:
sudo add-apt-repository ppa:webupd8team/nemo sudo apt-get update sudo apt-get install nemo nemo-fileroller
To launch Nemo, search for "Nemo" in Dash - no application called "Nemo" will show up but instead an application called files should be displayed - that's the app you need to launch. Don't search for "Files" because that will also find Nautilus (which is also called "Files").
Why use Nemo? Well, Nemo comes with a huge number of features that no longer exist in Nautilus (including treeview sidebar option). To see other tips like make Nemo your default file manager, etc. go to:
That feature got deleted from Nautilus by William Jon McCann. Reason:
Use a list model instead of a tree model
It is the list view after all. Tree models don't work well on touch and it isn't consistent with the file chooser.
Oh the changes made to Nautilus to remove it are in the link so feel free to fork Nautilus and re-install that alteration. Or pick another file manager (see the other answer)
I have Nautilus version 3.14.3
You can get something like "Tree view" with next steps:
See more detailed answer here: https://askubuntu.com/a/519188/586427