Below are some of the important and top must know Linux commands:
List directories
ls
Current working directory
pwd
Change directories
cd
Active user name
whoami
Special privileges
sudo
Display active processes
ps
Search for a string
grep
Display file contents
cat
Create directories
mkdir
Move or Rename files
mv
Copy files
cp
Remove files
rm
Print text
echo
Clear display
clear
Mount file systems
mount
Create Secure Shell Session
ssh
Check if 2 files are identical
cmp
Check what the command does
whatis
Locate Command source
whereis