The /proc directory is a way to view information on the running processes and the kernel within the file system.
/proc/[pid]/
For each process on the computer, there is a directory containing files with information on it.
/proc/[pid]/cmdline
This is a file that contains the command that started this process.
For example, run ps and get the process id of the shell. Next, run cat /proc/[pid]/cmdline (pid being the shell's process id.) And you would see the command that started the shell (probably bash.)
/proc/[pid]/cwd
This is a symlink to the current working directory of the process
Now, run readlink -f /proc/[pid]/cwd with pid still being the process id for the shell, and you will see the directory you are currently in.
/proc/[pid]/exe
This is a symlink to the original executable
And now, run readlink -f /proc/[pid]/exe and you will get the location of bash (or what ever shell you were using).
/proc/version
This contains information on the current version of Linux and its compiling.
/proc/uptime
This contains how long the kernel has been running for in seconds.
This is just a bit of the information you could get from the /proc directory.