The Value is contained in list condition will let you restrict an Event based on a connected Event data. You will have to specify two parameters in order for the condition to work.

First parameter is the connected Event data Value where the second parameter, a comma separated list, should be found.

By selecting Referrer as Value and "facebook,twitter" in Comma separated list will restrict the Event to only trigger if the words "facebook" or "twitter" are found in the current referrer.

Note that this condition must always be wired to an Event data before you can select it as a parameter.

The condition is case-insensitive.

Further reading:

Creating your first events