less it’s a fundamental command if you work on the Linux terminal.
Doing a “man less” you can see:
NAME less - opposite of more
I love Gnu/Linux man pages, in this case it refer to more another command that do similar things (but less).
The Linux command less is similar to cat, but with less you can scroll the file instead of showing the file at once. With less command you can scroll up in the file as well as down, where with the Linux command more you can only scroll down the file.
In one of the first articles of Linuxaria i’ve posted a complete how to in 
Sometime it’s useful to do an assessment of what’s online on your network, probably you think to know every server and service running, but I had more than one surprise in the past, with “test server just plugged in for a short time”, “New test service” or worst, hacked machine that exposed “new service”.
Sometimes happen that you find a sequence of links, and so you should start to follow them to see exactly what command are you about to run, or the directory used in that symbolic link, or you can use readlink.