To use the Merging and Formatting, click on the gear icon on the fields that you want to configure.

You will see the Formatting and merging fields in the settings.

The formatting field is only available for certain fields that are supported. 

The Merging field is available for all fields. This is how to use the Merging field.

The fields are expressed in such a way {{ item['Field Name'] }}

For example:

1. Merging field Shipping Address 1 and Shipping Address 2. You will need to add in the formula as follow for each field

{{ item["Shipping Address 1"] }} {{ item["Shipping Address 2"] }}

2. Multiply Sum of Total Line Item Price with 2.35 by using a times filter with a value of 2.35.

{{ item["Sum of Total Line Item Price"] | times: 2.35 }} 

3. If you have a currency formatting applied to your source settings, then this formula will make sure that it will perform similarly to the previous example but with formatting retained. To retain source formatting, the value of the first and last filters must match with the currently applied formatting value.

{{ item["Sum of Total Line Item Price"] | currency_to_number: "#.###,###" | times: 2.35 | number_to_currency: "#.###,###" }}

4. Conditionally override a field based on its original value

{% if item["Shipping Country"] contains "United Kingdom" %}
{% elsif item["Shipping Country"] contains "United States" %}
{% elsif item["Shipping Country"] contains "Britain" %}
{% endif %}

5.  Exporting the simple date format for the order 

{{ item["created at"] | date: "%Y %m %d" }}

Year (2016-07-01)
month (2016-07-01)
day (2016-07-01)
Hour (22:13:23 > 24 hours)
%MMinute  (22:13:23)
Second (22:13:23)

Click here to know more regarding the date format

6. Currency / Weight Conversion

Example USD to Euro

{{ item["Total Price"] | divided_by: 1.2 }}

Example Gram to KG

{{ item["weight"] | divided_by: 1000.0 }}

To know what filters are supported and more, explore here