ls
- List directory
cd
- Change directory
cat
- Concatenate - Easy way to print out a file. Best for small files
less
- Easy way to view larger files
Use an IDE if you like, but I recommend learning either Vim or Emacs. They are the holy relics of computer science. They have a steep learning curve, but once you master it your productivity will be 10x that of someone on an IDE.
For the meantime, just use an IDE that lets you code and jump into Vim or Emacs when you really start to get serious. They are worth the time investment.
I use Vim, but if I'm using an IDE I'll try and find an add-on that has Vim key-bindings.