Minimal code to create an admin/backend module in Magento2
etc/adminhtml/menu.xml
etc/adminhtml/routes.xml
etc/adminhtml/menu.xml
Controller/Adminhtml/SampleOne/Index.php
Controller/Adminhtml/SampleTwo/Index.php
view/adminhtml/layout/adminsample_sampleone_index.xml
view/adminhtml/templates/sample/one.phtml
view/adminhtml/layout/adminsample_sampletwo_index.xml
Controller/Adminhtml/SampleTwo/Index.php
view/adminhtml/templates/sample/two.phtml
Controller/Adminhtml/SampleTwo/Index.php
etc/adminhtml/system.xml
Configuration menu in Stores/Settings/Configuration is set hereetc/config.xml
Default configurationview/adminhtml/templates/sample/two.phtml
etc/acl.xml
etc/adminhtml/menu.xml
view/adminhtml/layout/adminsample_sampletwo_index.xml
Block/Adminhtml/CustomBlock.php
view/adminhtml/layout/adminsample_sampletwo_index.xml
Block/Adminhtml/CustomBlock.php
view/adminhtml/templates/custom/one.phtml
Block/Adminhtml/CustomBlock.php
Helper/ConfigHelper.php
view/adminhtml/templates/custom/one.phtml