As per the name of the feature it will modify the rate based on various condition for the shopify shipping rate.

You can set multiple rate modifier with single rate.

Here is the various conditions. Using that you can increase or decrees the rate of the shipping.

Order based condition:

• Day Of Order
• Time
• Price
• Weight
• Quantity
• Distance

Delivery based condition:

• Day
• X days from today
• Type

Product based condition:

• IDs
• Title
• Tag
• Type
• SKU
• Properties
• Vendor

Customer based condition:

• Zip Code
• Name
• City
• Address

Rate based condition:

• Rate

Once you choose the condition from the one of above.

You have to choose appropriate Operator like Equal, Does not equal, Greater than or equal, Less than or equal.

Set the Behaviour of this rate modifier cause you can set multiple rate modifier in the same rate.

Set the Modify Type like Fixed, Percentage, Remove Rate, Show Only.

Finally set the Effect what you want with rate Increase or Decrease.