The central point is the Configuration Management Database. It contains all necessary information for the modules. You have two options to add content to the CMDB:
Most of the time it would be a combination of both.
Just download the "Agent" and install it on the machine. If you like to install it unattended, you can add the parameter /S to the installer. If you have a bigger environment, an automated installation would be suggested. See here.
The "Agent" tries to get as much data as possible from the machine. But a CMDB should have more data than the pure hardware / software inventory. e.g. Commercial informations like warranty, assignment to persons etc.
If you need to add the same information to more than one device, please read the chapter MultiEdit. e.g. add the same "Warranty Date" to a bunch of new ordered Notebooks.
On Devices with an "Agent", you have the possibility to execute jobs on them. This could be for example:
You can join your network infrastructure with the CMDB. This is done via dot1x authentication. So only devices which are in your CMDB are allowed to get network access.