Filter entries by tags
You can read about how to use Relations in the docs. All relations such as (Tags) can be fetched via relatedTo parameter in your ElementsQuery

{% set tagId = craft.app.getRequest().getQueryParam('tagId') %}
{% set entries = craft
    .entries
    .section('faq')
    .relatedTo(tagId)
    .all() 
%}


This assumes you include the parameter tagId when someone clicks on your Tag, and that represents the ID of your Tag

{% for tag in craft.tags.group(1).all() %}
    &lt;a href="?tagId={{ tag.id }}"&gt;{{ tag.title }}&lt;/a&gt;
{% endfor %}