I know it might be a stupid question, but i'm confused ...
Is the input signal here a voltage signal or current signal ? and how can we produce two signals from one signal ?

 

Is the input signal here a voltage signal or current signal ?

both.

and how can we produce two signals from one signal ?

the same way that one answer can mean different things to different people.

 

The line from Vcc/Rc to Vcc is what;s called a "load line" which is a resistance, Note the axes are labeled Vce and Ic.

The "input signal" is across a resistance which is a voltage. From that there is an output voltage and output current. The "input signal" is impressed across the "load line" so it's not really a voltage or current. It's more of a V and I point (resistance). We generally don't think of things that way.

The highlighted "dot" is the operating point that was selected.

What your also seeing as a result of the multiple "blue lines" is the result of a "curve tracer" where the waveform is "stepped" to see a family of curves.

You can see that in Figure 5, here: http://www.onsemi.com/pub_link/Collateral/2N3055-D.PDF Flip the axes.

 

can we have a pure current or pure voltage?

 

Yes. A pure voltage the way I think you mean it is for example a battery without any load - it has voltage but no current is flowing.
A pure current in this sence would be for example in the main field coils in a MRI machine, where current is flowing through a superconductor, so there is current but no voltage between any parts of this coil.

 

can we have a pure current or pure voltage?

yes, to the extent you have pure conductors and pure insulators.