How to prepare a proguard file and whats included in it?

I am working on an app in Android Studio and I want to add proguard to my app. But I dont know what to do? Also I'd like to learn its context. Can anyone show me something? Thanks.

In your gradle file set true to minifyEnabled

You can define if proguard is enabled in debug, release or both

buildTypes {
        release {
            minifyEnabled true
            proguardFiles 'proguard-rules.pro'
        }
        debug {
            minifyEnabled false
            proguardFiles 'proguard-rules.pro'
        }
    }

You can also set the proguardFiles to configure it, check this site to see the docs about it, look this example:

# Add project specific ProGuard rules here.
# By default, the flags in this file are appended to flags specified
# in /Users/balysv/Documents/Android/sdk/tools/proguard/proguard-android.txt
# You can edit the include path and order by changing the ProGuard
# include property in project.properties.
#
# For more details, see
#   http://developer.android.com/guide/developing/tools/proguard.html

# Add any project specific keep options here:

# If your project uses WebView with JS, uncomment the following
# and specify the fully qualified class name to the JavaScript interface
# class:
#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
#   public *;
#}

-optimizationpasses 5
-dontskipnonpubliclibraryclasses
-dontskipnonpubliclibraryclassmembers
-dontpreverify
-verbose

If you want use a custom dictionary for code obfuscation, set this config with your dictionary file:

-obfuscationdictionary proguard-dic.txt
-classobfuscationdictionary proguard-dic.txt
-packageobfuscationdictionary proguard-dic.txt

The dictionary file is a simple text file with the labels you want to use to obfuscate your code, 1 label per line.