Let's make sure you followed the correct path when you used the terminal. You should have entered commands like this:
After you enter the first command you'll be prompted for your password, the same one you use to log into Ubuntu.
sudo apt-get update
sudo apt-get install libreoffice thunderbird
"Sudo" runs commands with the privileges of the "superuser" ("super user do"), known as the "root" user on Unix derivatives like Linux. Adding and removing packages is one task that only the root user can do.
Both commands use a program called "apt-get" to manage your installed software. The first command tells apt-get to check with all the "repositories" where Ubuntu software resides and update its lists of the most recent packages. The next line installs LibreOffice and Thunderbird.
If you want to know whether a package is installed, use the command "dpkg -s package_name" like "dpkg -s thunderbird". You will get back a lot of information if it installed, none if it is not.
When you install packages they will insert themselves into the program menu. If Thunderbird is installed, it will appear in the "Internet" section of the menus. LibreOffice unsurprisingly appears in the Office category.