How to install software in trisquel 7?

i am here new to linux.
i want to add some sofwares as per my requirements like google chrome web browser.

i tried to install it via apt-get install command but its seem not working and keep on saying
"E:Unable to locate package."

i don't what "E:" here stand for. is it my E drive?

After that i tried manually installing,
I downloaded .deb file of chrome from its official website.

and tried via installing and installed but with errors. its worked but system says package is broken.I also tried to repair via synaptic but there is only option of remove package. after it whenever i try to update my system then it says "first repair your broken packages".

so i wanna know how to install 3rd party software via terminal and also with synaptic package manager. i also heard of source file but don't know where it is and how to make use of it.

Thanking you for your time and concern.

AllegatoDimensione
1.png148.41 KB
2.png181.78 KB