My first operating system were Windows 3.1 and DOS as well as Windows 98. So as I took my first steps in Linux I had some problems. This cheat sheet should make everyone's life more easy. Some commands may differ if you use a Linux which doesn't belong to the Debian family.
The most basic commands every Linux user should know are probably:
cat, cd, cp (-a), chmod (-R), df (-h), du (-hs), grep (-i)(-r)(-v), gzip (-l), history, less, ln (-s), ls (-ahl)(-t), man, mkdir, nano (-c), rm (-r), tar, unzip, wget, whatis
The minimal set for the admin should be
chown (-R), crontab (-e), dd, dmesg (-T), head, htop, ip (a), kill (-9), lsblk, lscpu, lspci, lsof, lsusb, mount, passwd, ps (aux)(axjf), rsync (-aP)(-n)(--delete), scp, ssh, su, systemctl, tail, useradd, usermod, zipFor detailed informations about the commands check the manpages.
Additionally you should know these shortcuts
Print a file tree with all data like ls -lh
tree -pughDhide indentation
tree -pughD -ifull (relative) path
tree -pughDi -fonly dirs but 2 levels
tree -pughDif -d -L 2
For editing text files the most easy way is to use nano (nano /file).
But you will see some sadists who use vim (aka vi, read more here). The most important thing you need to know about it is you can "write-quit" it with the command :wq