While the Raspberry Pi's operating system is Linux, that doesn't necessarily mean you should go out and memorise every Linux command. The Pi is a different type of computer that's used for different kinds of projects, so the most useful commands differ from what you'd use on an everyday Linux machine. Over at Circuit Basics, they tallied up their 42 most used commands.
While a few of these commands are Raspberry Pi specific, like
raspi-config, most are just normal Linux commands. Still, some of these are commands you'll be running all the time on a Raspberry Pi, like
ifconfig which shows you the status of your network connect, or
hostname -I which grabs your Pi's IP address. These are the kinds of commands you'll be using a lot when setting up a new Pi, so it's useful to memorise them. Head over to Circuit Basics for their full list.