Explanation of Deprecation Warnings Why is this depreciated? Is there an example of the preferred method? 


  Looping through element queries directly has been deprecated. Use the all() function to fetch the query results before looping over them.


Thanks.
It means you've got a loop on an element query somewhere in your templates.  For example:

{% for entry in craft.entries.section('mySection') %}
    {{ entry.title }}
{% endfor %}


You should update it to use .all() like so:

{% for entry in craft.entries.section('mySection').all() %}
    {{ entry.title }}
{% endfor %}