1. useful commands

• ls
  show all files under current directory
• ls -a
  list all the files including hidden files (filename begins with dot)
• ls -l
  list files with more information(permissions, owner, size...)
• mv
  rename files or move them to a different directory
• cat
  read data from file and give their content as output
• touch
  create new empty file

2. explainshell.com

• great resources for looking up commands and usages