retrieve matrix data to twig file I create a section clientSection which I linked an matrix field like in this image:

The field has two block types : clientImage which has an field clientImage and clientDescription which has an field with same name.
I want to output in twig file but I don't know how exactly

{% set clients = craft.entries.section('clientSection').all() %}

{% for client in clients %}
  {# display content here #}
{% endfor %}


Thank's
You will need to use your Matrix field handle (which you didn't show in your question) and replace yourMatrixFieldHandle:

{% for client in clients %}
    {{ client.title }}

    {# Get all blocks related to the client entry #}
    {% for block in client.yourMatrixFieldHandle.all() %}

        {% switch block.type %}

            {% case "clientImage" %}

                {% for image in block.clientImage.all() %}
                    &lt;img src="{{ image.getUrl() }}" alt="{{ image.title }}"&gt;
                {% endfor %}

            {% case "clientDescription" %}

                {{ block.clientDescription }}

        {% endswitch %}

    {% endfor %}

{% endfor %}


Read more about working with Matrix fields here