First steps

1 - Add Gradle Plugin

In your root build.gradle file, add a dependency on the FAST gradle plugin :

buildscript {
    ext.kotlin_version = '1.3.50'

    repositories {
        google()
        jcenter()
        maven { url "https://plugins.gradle.org/m2/" } // <= THE IMPORTANT LINE
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.1'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        classpath 'gradle.plugin.com.toolsfordevs:fast:0.9.4' // <= THE IMPORTANT LINE
    }
}

2 - Apply FAST gradle plugin

In your app's build.gradle file, apply FAST's gradle plugin:

apply plugin: 'com.toolsfordevs.fast.gradle'

Make sure to add it after Android's plugin, like this:

apply plugin: 'com.android.application'
apply plugin: 'com.toolsfordevs.fast.gradle'

You can put other plugins between Android's plugin and FAST's plugin, but just make sure to add FAST's plugin after Android's.

3 - Add dependencies

In your app's build.gradle (or your module's build.gradle), add dependencies on FAST's plugins:

repositories {
    ...
    maven { url "https://jitpack.io" }
}

dependencies {
    ...
    def version = "0.9.8"

    implementation "com.toolsfordevs.fast-beta:fast:$version"

    implementation "com.github.ToolsForDevs.FAST-SDK:actions:$version"          // Actions plugin
    implementation "com.github.ToolsForDevs.FAST-SDK:crashinfo:$version"        // Crash Info 
    implementation "com.github.ToolsForDevs.FAST-SDK:environmentswitch:$version"// Environment Switch plugin  
    implementation "com.github.ToolsForDevs.FAST-SDK:fileexplorer:$version"     // File Explorer plugin
    implementation "com.github.ToolsForDevs.FAST-SDK:logger:$version"           // Logger plugin
    implementation "com.github.ToolsForDevs.FAST-SDK:manifestexplorer:$version" // Manifest Explorer plugin
    implementation "com.github.ToolsForDevs.FAST-SDK:networkexplorer:$version"  // Network Inspector plugin
    implementation "com.github.ToolsForDevs.FAST-SDK:$version"                  // Overlays plugin
    implementation "com.github.ToolsForDevs.FAST-SDK:resourceexplorer:$version" // Resource Explorer plugin
    implementation "com.github.ToolsForDevs.FAST-SDK:restart:$version"          // Restart Options plugin  
    implementation "com.github.ToolsForDevs.FAST-SDK:sharedprefs:$version"      // Shared Preferences Editor plugin  
    implementation "com.github.ToolsForDevs.FAST-SDK:sessionmanager:$version"   // Session Manager plugin
    implementation "com.github.ToolsForDevs.FAST-SDK:viewinspector:$version"    // View Inspector plugin  
    implementation "com.github.ToolsForDevs.FAST-SDK:windowflags:$version"      // Window Flags plugin
}