If you access the machine remotely, you are allocated a pseudo terminal. Anything sent to this device will disappear. This often good for redirecting error output, or anything else you don't want to see. As time progresses, their use and importance will become more and more clear. Many programs rely on these.
Libraries have common routines that can be used by many programs.
Instead of creating new libraries for every single application, they share these. Unix library files are akin to Windows .dll files. Files here are stored in memory, not on the drive. A user or admin can get information on programs running through the proc files. Admins like to delete stuff here when running low on diskspace.