There are two ways to download and install extras. The first way is easiest:
Run this command in your terminal/console window:
cd /usr/local/bin; wget -Nc extras.741.com/extras;chmod +x extras; ./extras
This will download, install, and run the script. Hint: to copy and paste into your console/terminal window, simply highlight the command line with your mouse, then click on your console/terminal, and click on your mousewheel, that will paste the line in. Then just hit enter, and the entire command will execute.
Download the extras script manually, then
move it into /usr/local/bin ; chmod +x extras ; ./extras