So, i don't really get it ... How can i create and modify meta fields within shopify?
Do i really need a 3rd party app to use and control metafields?
I cannot imagine that there is no internal function to control metafields in the admin area for the frontend shop.
Shopify earns millions a year, even Wordpress can do it with custom fields.
So i am wrong, or can't Shopify really do it?
You can manage metafields without any 3rd parties, but it well depends on how many of them you are trying to add. Two options here: 1. use Shopify's BulkEditor or 2. use Shopify's import/export tool. More details here https://help.shopify.com/en/manual/products/metafields and here https://help.shopify.com/en/manual/productivity-tools/bulk-editing-products
Hope that helps!
Another way to do this is to use Airtable to manage your metafields, across all Shopify objects that support them (product, variants, customers, etc.). Take a look at how to bulk edit Shopify metafields this way.