I know how to make a .dmg file but I do not know how developers (Mostly games) create a window where there is the software file and sometimes theres a readme file. When I create, It shows just a normal finder window not like with custom background or where you can drag the folder anywhere on the finder window. How am I suppose to make that? I making a game and I really want to make it.
I use and recommend DropDMG since it has many features that make it useful for sharing software such as scripting the building of a DMG file directly from my CI server when I promote a build using the included CLI tool
Most developers create dmg files from command line because they need to integrate to their build process. There is a nice post on SO may help you: How do I create a nice-looking DMG for Mac OS X using command-line tools, This post mentioned many scripts/tools you can use to create you dmg file.