app/code/Foo/Bar/etc/frontend/routes.xml

<?xml version="1.0"?>
<!--
Place this file in either the "frontend" or "adminhtml" folder to define either
a frontend or admin route, respectively.

The "urn:magento:framework:App/etc/routes.xsd" file is used to validate this
XML file. You can inspect it at vendor/magento/framework/App/etc/routes.xsd
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:App/etc/routes.xsd">
    <!--
    The "standard" router is used to handle standard frontend requests.
    Set the id to "admin" to create a backend admin route.
    -->
    <router id="standard">
        <!--
        The "id" attribute is used as a unique key for this node. It should
        almost always match the value of "frontName" for consistency reasons.
        Its value cannot contain dashes, so underscores can be used instead.

        The "frontName" is used to catch incoming requests. This route listens
        for requests being made to: /my-route/*/*
        -->
        <route id="my_route" frontName="my-route">
            <!--
            The "route" node looks for "module" nodes with "name" attributes.
            These are the modules responsible for handling these requests.
            -->
            <module name="Foo_Bar"/>
        </route>
    </router>
</config>