Media items from the media tab are stored as json objects in an array on pages in the media property. To display them all, you might do this:

{% if %}
{% for image in %}
  <img src="{{ image.url }}" alt="{{ image.caption }}" />
{% endfor %}
{% endif %}

To display the first one, you might do this:

<img src="{{[0].url }}" alt="{{[0].caption }}" />

Typically with images you'll want to use the image resizing filter.