Create a simple module for Drupal 8 - Step 1

Module name : Test

Step 1. Create the module folder on module/custom directory
Exemple : module/custom/test

Step 2. Create info file on the root of the module folder (module/custom/test/test.info.yml) and configure. File name must be ModuleName.info.yml
Exemple :
name: Test Module
description: 'Short description'
type: module
core: 8.x
version: TheVersion

Step 3. Activate the module
On  admin/modules
Or using drush en test -y

Note : Here the minimum to create a module