Arguments are defined within the macro search string by using dollar signs on either side of the argument name, such as arg1 or fragment.
References
Search macro examples
Define search macros in Settings
Use search macros in searches

The transaction command is a search command that creates a single event from a group of events that share some common characteristics. The transaction command can group events based on fields, time, or both. The transaction command can also create some additional fields for each transaction, such as duration, eventcount, startime, etc. The transaction command does not group a set of transactions based on time, but rather groups a set of events into a transaction based on time. The transaction command does not separate two events based on one or more values, but rather joins multiple events based on one or more values.
The transaction command does not return the number of credit card transactions found in the event logs, but rather creates transactions from the events that match the search criteria.

Tags are a knowledge object that allow you to assign an alias to one or more field values . Tags are applied to events at search time and can be used as search terms or filters .
Tags can help you make your data more understandable by replacing cryptic or complex field values with meaningful names . For example, you can tag the value 200 in the status field as success, or tag the value 404 as not_found .

https://docs.splunk.com/Documentation/Splunk/8.1.1/SearchReference/ConditionalFunctions