You can do most (if not all) of your computing activities not touching the
terminal. For example, if you want to understand what eats up space on your
disk, you can use GNOME's "Disk Usage Analyzer" that shows you some kind of
pie diagram, every slice corresponding to the space occupied by a folder
(clicking on such a slice details the space occupied by its sub-folders).
That said, command lines often are convenient. Especially when helping: it is
far easier to write "execute this command" than "if you have this version of
this graphical application then click on this, then on that, then...".
I believe you are making confusion between two different kinds of memory: the
disk and the RAM. Disks (such as hard drives, flash drives, memory cards,
etc.) are permanent storage: switching off the computer, they are not
emptied. This is where your files and the system files are. The RAM (as well
as CPU cache, the whole being named "main memory") is a much faster kind of
memory, e.g., 100 times faster to read/write. It is more expensive too. When
executed, the programs (e.g., your movie player) are first copied from the
disk to the RAM, where they also copy there the data they work on (e.g., the
movie itself). When the computer is switched off, the RAM is emptied.
I believe you have 2 GB of RAM but were looking at the space left on a
partition of your hard drive.
The the GNOME edition of Trisquel, the "System Monitor" in the "System
Settings" allows to graphically observe how much RAM is used (second diagram
in the second tab, "Resources"). The last tab, "File Systems", gives the
overall usage of the partitions of your disks. For a finer analysis, there is
the "Disk Usage Analyzer" I mentioned I the beginning of this post.
By default, Trisquel Mini includes neither tool. I do not know if it includes
alternatives. Anyway, you can install the two tools, e.g., from the "Synaptic
Package Manager". The packages are named "gnome-system-monitor" and "baobab".
The folders that "mystify" you are normal. Some system folders can only be
"traversed" by the system administrator, i.e., the user you become when your
password is asked (e.g., when launching the "Synaptic Package Manager").
"lost+found" is used by some "filesystems" (the format files are stored in a
partition of a disk). When such a filesystem is "checked", e.g., after an
abrupt shutdown (what can entail a file loss), some files that are "found"
are put in the folder "lost+found" (at the root of the filesystem) because
their names and locations cannot be restored. So, if, "lost+found" is not
empty, you can find in it data that you have lost (e.g., because of a power
I hope that you better understand your system thanks to my explanations. That
said, to solve a specific problem, you had better precisely describe it (and
only it), reply to what we ask you (such as output of commands) and not open
parentheses inside parentheses. Personally, I still do not understand the
problem you actually face.