How do I expose a contextual filter? I have created a view that shows few entities. To be able to see only a particular entity, I created a contextual filter.

How can I expose the contextual filter I added?
Contextual filter is an an argument to the view, for example through the path or block/plugin context.

It is not visible to the user, it's visible to Drupal.

If you want something to be visible to the user, you need to instead add a filter and then tick the checkbox to expose it, creating a so called "exposed filter". That should then show up in a filter form.