Can't install awesome software

Have you tried through Synaptic?

"deb http://deb.torproject.org/torproject.org trusty main" is a repository. Not a command. Here is the command to add the repository:
$ sudo add-apt-repository "deb http://deb.torproject.org/torproject.org trusty main"

tor website - download tor browser bundle - download gpg signature.

add the tor developers gpg key.
verify the tar with the sign.

extract and run the executable.

I suggest you don't add the tor repository to Trisquel because Trisquel doesn't use the package from ubuntu's repos. If you check the code in the package helpers you will see that the tor version included is the latest provided by the tor developers and not Debian nor ubuntu.

Here's an estract:

EXTERNAL='deb-src http://deb.torproject.org/torproject.org trusty main'

In other words: you only need to "sudo aptitude install tor" and that's it

For the tor browser, follow the indications provided by that the other members have provided you.

> "deb http://deb.torproject.org/torproject.org trusty main" in the terminal
> the only output i get is "bash: deb: command not found"

What you were trying to enter in the terminal is actually a source
specification line for APT (the package management system). It is not a command
to be run in a terminal, but rather a line to be added
to /etc/apt/sources.list. This then lets the system know that it should fetch
packages from that server, as well as the others. An apt-get update is required
so that the system knows of the new packages available for installation after
the new source repository has been added.

Adding that line to your sources.list would have told the system to fetch
packages from that server in future. You could then install the Tor packages
and have them updated over time. However, as the other posts here indicate,
that would not be a very good way of going about things. Besides, the official
tor repository only contains tor itself, and not the Tor Browser, which is
probably what you want. You can download the latest version for your system
here: https://www.torproject.org/download/download.

For I2P you'll find instructions here: https://geti2p.net/en/download