Create a container for new block - Magento 2

When adding block in layout file, declare our container before block declaration.

<container name="some.container" as="someContainer" label="Some Container" htmlTag="div" htmlClass="some-container" />
...
Block code comes here
...
</container>

The above code will create a DIV container for content from block with CSS class some-container. The htmlTag will be a div, ul, span etc any HTML element.