The example below describes how to declare three different types of direct dependencies in the app/ module's build.gradle file:

   android {...}
    ...
    dependencies {
        // The 'compile' configuration tells Gradle to add the dependency to the
        // compilation classpath and include it in the final package.
    
        // Dependency on the "mylibrary" module from this project
        compile project(":mylibrary")
    
        // Remote binary dependency
        compile 'com.android.support:appcompat-v7:24.1.0'
    
        // Local binary dependency
        compile fileTree(dir: 'libs', include: ['*.jar'])
    }

To download dependencies, declare the repository so Gradle can find them. To do this, add a repositories { ... } to the app/ module's build.gradle in the top-level file.

repositories {
  // Gradle's Java plugin allows the addition of these two repositories via method calls:
  jcenter()
  mavenCentral()

  maven { url "http://repository.of/dependency" }

  maven { 
      credentials {
          username 'xxx'
          password 'xxx'
      }

  url 'http://my.maven
  }
}

In a multi-project gradle build, you can have a dependency with another module in your build.

Example:

  dependencies {
        // Dependency on the "mylibrary" module from this project
        compile project(":mylibrary")
  }

The compile project(':mylibrary') line declares a local Android library module named "mylibrary" as a dependency, and requires the build system to compile and include the local module when building your app.

You can have a dependency with a single jar or multiple jar files.

With a single jar file you can add:

dependencies {
    compile files('libs/local_dependency.jar')
}

It's possible to add a directory of jars to compile.

dependencies {
        compile fileTree(dir: 'libs', include: ['*.jar'])
}

The compile fileTree(dir: 'libs', include: ['*.jar']) line tells the build system to include any JAR files inside the app/libs/ directory in the compilation classpath and in the final package of your app.

If you have modules that require local binary dependencies, copy the JAR files for these dependencies into <moduleName>/libs inside your project.

If you need to add an aar files you can read more details here.

You can add remote dependencies in Gradle usign this structure:

compile 'group:name:version'

or this alternative syntax:

compile group: 'xxx', name: 'xxxxx', version: 'xxxx'

For example:

compile 'com.android.support:appcompat-v7:24.1.0'

The compile 'com.android.support:appcompat-v7:24.1.0' line declares a dependency on version 24.1.0 of the Android Support Library.

Dependencies can be added for specific configuration like test/androidTest

androidTestCompile 'com.android.support.test.espresso:espresso-core:2.2.1'
testCompile 'junit:junit:3.8.1'

Alternatively create your own configuration

configurations {
    myconfig
}

And then download dependency for this config

myconfig group: 'com.mycompany', name: 'my_artifact', version: '1.0.0'

Dependencies can be added for specific product flavors in a similar fashion as build configurations.

android {
    ...   
    productFlavors {
        flavor1 {
            //...
        }
        flavor2 {
            //...
        }
    }
}

dependencies {
    flavor1Compile 'com.android.support:appcompat-v7:24.1.1'
    flavor1Compile 'com.google.firebase:firebase-crash:9.4.0'
        
    flavor2Compile 'com.android.support:appcompat-v7:24.1.1'
} 

Dependencies can be added for specific Build types:

android {
    ...   
    buildTypes {
        release {
            //...
        }

        debug {
            //....
        }
    }
}

dependencies {
    debugCompile 'com.android.support:appcompat-v7:24.1.1'
    releaseCompile 'com.google.firebase:firebase-crash:9.4.0'            
}