repositories declaration inside build.gradle

I've been confused about the different repositories declaration inside build.gradle.

There are:

• repositories inside top-level build.gradle's buildscript block
• repositories inside top-level build.gradle's allprojects block
• repositories inside each module build.gradle's buildscript block
• repositories at each module build.gradle

Breaking down to 2 differences, repositories inside buildscript block and others.

inside buildscript block

The buildscript configuration section is for gradle itself (i.e. changes to how gradle is able to perform the build).
So the repositories here only affecting gradle building process.

inside top-level allprojects or module

The allprojects section is for the modules being built by Gradle, hence repositories inside the module is module specified.

This type of repositories is where your dependencies used to look up packages.