How add custom field to products without any paid app in Shopify?

There are many requirments to add custom data to the products but you can not add any custom fields without any app.
But there are a way to add custom fields to the products but this is not come to directly product edit page in admin.
But this gives you a new screen, where you can add custom datas direclty to the many products togather.

If our shopify store url is https://xyz.myshopify.com
then custom fields screen will be

https://xyz.myshopify.com/admin/bulk?resource_name=Product&edit=metafields.global.custom_fields_1%3Astring%2Cmetafields.global.custom_fields_2

You can see there a variable “resource_name” used, it denotes that for which resouce type we are adding custom fields.
You can also see custom_fields_1 and custom_fields_2 are two custom fields keys are used, you can use this keys as you want but every keys will be unique.

By above url you can see screen some thing like this

After adding custom fields, you can get this fields values by using this

I hope this will help you?

HAPPY CODING!