This is a deceptively hard question! If you look up the Technet page regarding the Actions tab, you'll find that it tells you nothing about each action. All of the actions on the tab are scheduled tasks; that is, if the feature is enabled, it will automatically run on a periodic basis. In some circumstances (e.g. troubleshooting), you may find the need to manually initiate these tasks. That's where this tab comes in. The information on each action's functionality is scattered about the Technet website (although I understand and personally use many of the these actions, I copied from the Technet website because I'm lazy):
Branch Distribution Point Maintenance Task verifies any prestaged packages and downloads any that do not exist on the branch
distribution point. While Technet does not explicitly state it, I
believe this task is useful only on branch distribution points and is
ignored on normal clients.
Discovery Data Collection Cycle causes the client to generate a new discovery data record (DDR). When the DDR is processed
by the site server, Discovery Data Manager adds or updates resource
information from the DDR in the site database.
File Collection Cycle When a file is specified for collection, the Microsoft System Center Configuration Manager 2007
software inventory agent searches for that file when it runs a
software inventory scan on each client in the site. If the software
inventory client agent finds a file that should be collected, the file
is attached to the inventory file and sent to the site server. This
action differs from software inventory in that it actually sends the
file to the site server, so that it can be later viewed using Resource
Explorer. This is a part of SCCM inventory functionality.
Hardware Inventory Cycle collects information such as available disk space, processor type, and operating system about each
computer. This is a part of SCCM inventory functionality.
Machine Policy Retrieval & Evaluation Cycle The client downloads its policy on a schedule. By default, this value is
configured to every 60 minutes and is configured with the option
Policy polling interval (minutes). However, there might be occasions
when you want to initiate ad-hoc policy retrieval from the client—for
example, in a troubleshooting scenario or when testing. This action
initiates ad-hoc machine policy retrieval from the client outside
its scheduled polling interval.
Software Inventory Cycle collects software inventory data directly from files (such as .exe files) by inventorying the file
header information. Configuration Manager 2007 can also inventory
unknown files — files that do not have detailed information in their
file headers. This provides a flexible, easy-to-maintain software
inventory method. You can also have Configuration Manager 2007 collect
copies of files that you specify. Software inventory and collected
file information for a client can be viewed using Resource Explorer.
This is a part of SCCM inventory functionality.
Software Updates Scan Cycle Just after a software update installation completes, a scan is initiated to verify that the update
is no longer required and to create a new state message that indicates
the update has been installed. When the installation has finished but
a restart is necessary, the state will indicate that the client
computer is pending a restart.
User Policy Retrieval & Evaluation Cycle Similar to Machine Policy Retrieval & Evaluation Cycle, but this action initiates
ad-hoc user policy retrieval from the client outside its scheduled
Windows Installer Source List Update Cycle causes the Product Source Update Manager to complete a full update cycle. When
you install an application using Windows Installer, those Windows
Installer applications try to return to the path they were installed
from when they need to install new components, repair the application,
or update the application. This location is called the Windows
Installer source location. Windows Installer Source Location Manager
can automatically search Configuration Manager 2007 distribution
points for the source files, even if the application was not
originally installed from a distribution point.
I also found this explanation for the Application Deployment Evaluation Cycle:
Application Deployment Evaluation Cycle – This action re-evaluates the requirement rules for all deployments. If an application is required, and not installed when the Application Deployment Evaluation Cycle runs, Configuration Manager automatically triggers a re-install. The Application Deployment Evaluation Cycle only applies to applications and not to the packages. The default value is set to run every 7 days.