The data import feature for the ROOKIE (free) plan is available on app credits basis. 

You can learn more about our plans and the app credits here ;)

First, go to the app section of your Shopify admin panel: 

and select our awesome app:

Next, go to "Bulk actions -> Import": 

Once there, you can select the resource type you'd like to import the metafields for from a drop-down menu:

and click "Continue" button to move to the next step.

On the next screen, you can upload a CSV file containing the metafields you ant to import:

Haven't got a file yet? Don't worry, you can get a template file by clicking the "Download template file" button.

Great, once the file is uploaded, hit the "Continue" button to proceed to the fields mapping step:

Now, the most important part needs to be handled.
We need to map the fields from the file uploaded on the previous step to the fields required by Shopify to create the metafields.

As we learned earlier, the metafields object consists of three main components: 

1) namespace 

2) key

3) value 

Namespaces are used to group different metafields, keys are unique identifiers to reference the information stored in the metafields, and values will contain the the data itself.

In addition to this, the file should contain either the id or a handle for the resource you want add the metafields to. You can learn more about the Shopify object and their properties here.

Now, let's sort out the controls:

1) The list of the required fields that need to be mapped.

2) This switch allows you to use the first row of the file as a header. This is a pretty handy thing that makes the mapping a little faster and easier. 

3) This switch allows you to choose the identifier of the resource to used -that additional field we discussed earlier. This can be either the id or handle (email, if we're talking about the customers).

4) The mapping section itself. Here you can choose a corresponding metafield attribute (namespace, key or value) for each of the fields presented in your file.

Once this step is completed, the import screen should look like this:

Click "Continue" button to move to the next step.

This page allows you to see some statistics for the future import: the resource type to be affected, the total number of the metafield to be imported, the file size etc. In addition to this, you can enable an option to remove the metafields featuring an empty value in your file. It comes really handy when dealing with the large amount of the data. Also, some users simply like to manage the data with the spreadsheets :)

Once you're sure all the settings are correct and you're ready to proceed - hit the "Start import" button and we're done :)