Learning how to use the terminal in Linux is essential, especially if you need to install apps that are not in your software center. A good tutorial can be found here.
Here’s a tutorial on how to install apps in a Linux terminal.
To install the GUFW firewall in terminal, use the following:
sudo apt-get install gufw
After install, read more on how to configure here.
To install Gimp image editor, use the following in terminal:
sudo apt-get install gimp
*Note: Gimp is available in most software centers.