**I have collected certain stamps from google I tried it once but i couldn't get it. Help me out........... **
There's already in a comment a proper receipe. You fill a layer with overlapping stamps which have transparent backgrounds. Insert a layer mask, fill it with black at first. Then paint white to the mask. That's effectively the same as you painted with stamps.
If you want to build your own fake stamps the job will be gigantic. You can buy a collection from some image stocker.
If you download images from web they can be copyrighted and you can collect harms by using them. The harms can start as soon as you distribute (=sell, upload, put generally visible or give for free to others) unlicensed stuff. Making an image to be watched and kept only in your home is harmless.
Image stockers have all different licensing practices of what you need to pay for different usage types. Read the license!