Change Documents

Hi Experts,

I know the transaction SWEC. Here We Can Give the Change Document for bossiness Object.

My Question is What is Change Document. Its a Program or Abap Class or anything Else?

We have Some standard Change documents like EINKBELEG for Purchase Order. Now I want to create a Change Document? Is it Possible?.

Possible means whats the Transaction Code?

Thanks in Advance.

Points Will Be Surely Rewarded.