When it comes to the Configuration database, Actions are the very foundation of both the Configuration database itself and MarvelClient in general.
Depending on the scope of license, the Configuration database allows you to instruct MarvelClient on your IBM Notes clients to carry out various tasks, such as housekeeping, optimization, configuration, initial setup, upgrades, audits, and much more, virtually covering all aspects of your client management demand. Since not all customers require all of MarvelClients features from the very start, MarvelClient is available in various different modules, each enabling different (sets of) Actions.
Actions can be deployed to all or certain users (including the option to again exclude a subset of users), tied to Conditions, and even made dependent on other Actions and results (see Action_alias here).
See Also
The MarvelClient Configuration database
About Conditions
Configuration basics - general fields in the header area of Actions
The What, When, Who and Admin tabs
About Runtypes
About References and Placeholders