The command line interface is run in a terminal (or prompt). It is the direct interface with your computer. There you are able to do the same things are you are able in a graphic interface such as visiting a folder, reading and writing files.
But the command line interface allows you access to a number of other programs which are really useful in a developer's every day life or while participating in CTFs. You should not be an expert, but with little knowledge of the command line you will already be able to do a number of things faster and quicker.
Terminals in Linux and OSX are quite similar, if you run Windows, things are a bit different.
Paths are the base of the structure of your operating system. You have to think of it like a tree (there is even a command to show you the whole structure of your folders called `tree` -- try it out!).
For example:
```
home folder
| sub folder
| | sub sub folder
| | file in sub sub folder.txt
| second sub folder
```
Your home folder (`/home/your_username`) is usually abreaviated by `~`. So for example the "Documents" folder in your home folder is marked as `~/Documents`. This is how the structure works for the example above:
```
home folder/sub folder/sub sub folder/file in sub sub folder.txt
You can feel like a real hacker from movies while just using your terminal. So this means you can run program in the command line. Already the few examples above are small programs. To run a program you have to write the name of the program you want to run and options and then press "enter" to run it.
Many programs have a manual to explain how to use them, you can access it by using the `--help` or `-h` option. Try typing: `cat --help` and then press enter in your terminal.
