show related products shopify

how to show related products shopify

{% assign vendor = product.vendor %}
{% assign handle = product.handle %}
{% assign counter = '' %}
{% for product in collections.all.products %}
{% if vendor == product.vendor and counter.size < 4 and handle != product.handle %}
{% capture temp %}{{ counter }}*{% endcapture %}
{% assign counter = temp %}
{% include 'product-grid-item' %}
{% endif %}   
{% endfor %}