Components and groups are both like wrappers you put geometry into. Once inside the wrapper the geometry is protected from interacting with anything else in the model. It becomes a distinct "object” that can be moved around and worked with. To make changes to that object you need to open the wrapper to reach inside and work with the geometry, by double clicking or right clicking and choosing edit. I particularly like @DaveR ‘s jelly bean analogy here.
The main difference is that groups are single instances of an object, while components can have multiple instances that are all linked. In your case I would use components to make up the individual parts of the pipe system as elbows, and valves etc are identical repeating parts. Then if you later make a small change to one of them the change will be reflected across all instances in the entire drawings, a real time saver. Once your geometry is enclosed in a wrapper it can then be assigned to a tag. So you might assign all the individual components of a given system to a single tag called “steam system 1”. Then you can easily control the visibility of that entire system with the tag window.
You could put each system into it’s own group or component also, this is called nesting, having wrappers within wrappers and is fine. It can take longer to edit if there is a lot of nesting because you have to drill down inside the wrappers to get to the thing you want to edit but it’s fine to do. If you are editing a component you can choose View>Component Edit>Hide rest of model to solo that component while editing.