The Raspberry Pi is a series of small single-board computers developed in the United Kingdom by the Raspberry Pi Foundation to promote the teaching of basic computer science in schools and in developing countries. They are low-cost, high-performance devices that people use to learn programming and build hardware projects, ranging from weather stations to robots.
Raspberry Pi Documentation - Raspberry Pi OS
How2Setup a Raspberry Pi for safe connection to the Internet - Simon The Pi Man
lsb_release -a
cat /etc/os-release
uname -a
hostnamectl
df -h
sudo apt update
sudo apt upgrade
env # print all environment variables
export MY_VAR="my_value" # set an environment variable
echo $MY_VAR # print value of environment variable
unset MY_VAR
htop # terminal monitor