This will be the first achievement you get in your campaign. Complete the first 5 (easy) missions you are given to get this achievement.
The missions are:
* Fresh Off the Bus - Basic tutorial.
* The Doctor Is In - Speak to Dr. Zed.
* Fix'er Upper - Fix the vending machine and buy a shield.
* Claptrap Rescue - Fix CL4P-TP.
* Skags at the Gate - Kill 5 skags.