I as for past Computer Science studies had to install (for free) Eclipse and Visual Studio 2015 Community So if all i will need are the corse libreries (and i can just install them on my computer ,if would know how..) Do i realiy need to install the Appliance? Cause i don't have my very own personal computer ( i am using the family one). But i can install programs like IDEs ,web servers and SQL servers unlike installing a new virtual machine or an actuall OS.
It would be advantageous to you for several reasons:
cs50.h is embedded within the appliance, this is a very useful bit of kit and is referenced upon for several weeks, it would take you a very long time to make this file yourself.
Stanfords portable library is also embedded within the appliance, you will need this for one of the psets.
the appliance has everything you need for this course built into it, It may be possible to do the course without it, but you'd be hitting problems all over the place.
Just go with the flow :)
You don't "need" to use appliance. It will make things easier for you though.
Here is a good thread describing how to install the tools and libraries needed for the course. It is specific to Ubuntu, but should give you a good starting point.