Why I can't find the SoftwareSerial library.And how to use the SomeSerial lib???

johnwasser:
Or maybe you are using an ANCIENT version of the Arduino IDE from before SoftwareSerial was added.

I doubt it.

Release Notes:

ARDUINO 0007 - 2006.12.25

...

  • Added a SoftwareSerial library ...

The oldest version you can download from arduino.cc is 0013.