How To get data from API in android studio tutorials -

API implementation steps :

Step 1 - Create Android Projects in Android Studio

Step 2 - Add internet Permission in Manifest file

<uses-permission android:name="android.permission.INTERNET"/>

Step 3 - Add Retrofit Library dependencies in build.gradle file for get response from API 
and converte json file

implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
implementation'com.squareup.retrofit2:retrofit:2.9.0'

Step 4 -Create a Model class DataModel.java to call  Api Response

public class DataModel {

}

Step 5 -  Create a class RetrofitInstance.java

public class RetrofitInstance {

    // STATIC INSTANCE FOR CALL ANYWHERE WITHOUT MAKE OBJECT
    private static Retrofit retrofit;
    // DEFINE YOUR BASE URL WHICH IS COMMON IN YOUR API
    private static String BASE_URL = "https://jsonplaceholder.typicode.com/";

    // CRETE A GETTER METHOD TO GET INSTANCE
    public static Retrofit getRetrofit() {
        // CONDITION FOR CREATE RETROFIT OBJECT
        if (retrofit==null){
            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create()).build();
        }
        return retrofit;
    }
}

Step 6- Create a new interface Class  ApiInterfaceEndPoint.java for ends points

public interface ApiInterfaceEndPoint {

    @GET("todos")
    Call<List<DataModel>> getData();

}

Step 7 - Call  Data from API in Your  in Activity 

Before onCreate Method  Create Retrofit instance

ApiInterfaceEndPoint apiInterface;

After Create Instance Write Code In onCreate  method

apiInterface = RetrofitInstance.getRetrofit().create(ApiInterfaceEndPoint.class);
apiInterface.getData().enqueue(new Callback<List<DataModel>>() {
    @Override
    public void onResponse(Call<List<DataModel>> call, Response<List<DataModel>> response) {
        if (response.body().size()>0){
            Toast.makeText(MainActivity.this, "List is not Empty", Toast.LENGTH_SHORT).show();



        }else {
            Toast.makeText(MainActivity.this, "List is Empty", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void onFailure(Call<List<DataModel>> call, Throwable t) {
        Toast.makeText(MainActivity.this, t.getMessage(), Toast.LENGTH_LONG).show();
    Log.d("error",t.getMessage());
    }
});

Medium guide - link 

API Making Tutorials - link

Implementation guide - link