Assuming that you are also new to linux you could casually read (and reference whenever you need):
-The Linux Command Line A Complete Introduction by William Shotts and
-How Linux Works What Every Superuser Should Know by Brian Ward
-g0tmi1k’s blog is a great place to learn about penetration testing stuff as a beginner.
Go to his oldest posts and start doing what he does.
Give it time and dont overflow your self with information