Error during Building an APK file in Android Studio 2.1.1

build.gradle file

apply plugin: 'com.android.application'

android {
signingConfigs {
}

compileSdkVersion 23
buildToolsVersion "23.0.1"

defaultConfig {
    applicationId "com.dovezeal.gapp"
    minSdkVersion 19
    targetSdkVersion 23
    versionCode 1
    versionName "1.0"
    multiDexEnabled true
}

packagingOptions {
    exclude 'META-INF/DEPENDENCIES'
    exclude 'META-INF/NOTICE'
    exclude 'META-INF/LICENSE'
    exclude 'META-INF/license.txt'
    exclude 'META-INF/notice.txt'
}
buildTypes {
    release {
        minifyEnabled true
        proguardFiles getDefaultProguardFile('proguard-android.txt')
    }
}

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_7
    targetCompatibility JavaVersion.VERSION_1_7

}

}

dependencies {
compile fileTree(include: ['*.jar'], dir: 'libs')
compile 'com.android.support:appcompat-v7:23.0.1'
//compile 'com.android.support:appcompat-v7:23.3.0'
compile 'com.android.support:support-v4:23.3.0'
compile 'com.android.support:design:23.0.1'
compile 'com.android.support:design:23.1.1'

// as you already compiled gradle for volley here

compile 'com.android.volley:volley:1.0.0'

// RecyclerView
compile 'com.android.support:recyclerview-v7:23.0.+'
compile 'org.lucasr.dspec:dspec:0.1.1'

// you don't need this so comment the below line.
//compile files('libs/library-1.0.0.jar')

// YouTube Player
compile files('libs/YouTubeAndroidPlayerApi.jar')

}

Edit : Explanations

Your errors 1 - 2 : mean you are having more than 65,000 methods in your project, so I told you to set multiDexEnable true.

Your error 3 : means you're having more than one library having the implementation for the class Request$Priority.class, so the compiler is confused which to choose. So it is showing the error Duplicate entry. This will be solved by packaging options, this will let you use duplicate files.