The Matrix can be thought of as the internet. They are very close analogues, and there is generally no case where they are different, aside from how they are viewed.
The differences between the Matrix and the internet are more low-level, existing with concepts such as ownership, and daisy chaining connections. For example, if you connect to a node, and attempt to connect from that node to another node, your access id is sent, which may let you be traced, unlike the real internet in which it would appear to come from another servers ip address.
Nodes can be thought of as the publicly accessible webpage of a server, a device would be the server itself. See page 224 for the exact definition, but the point is that every online device creates a node in the Matrix.
Page 224 under "Subscriptions" clearly lists how talking to a node works. If you are within mutual Signal range, connected directly, or by being routed through the matrix you may access a node.
Unwired has rules on Noise that effect the last option, but without those rules there is no downside to routing. This means you can access any node from anywhere, with the Noise rules providing some penalties based on distance. You may access a node from anywhere, with some Data Transport restrictions. Most commonly everything is hooked up either wirelessly or using Fiberoptic Lines - in this case, you can assume no interference. Unwired specifically states:
In both radio signals and fiberoptic cables, electromagnetic waves are
used to transport data at extremely high speeds. A data request can
easily make a trip to the other side of the world and back within 0.2
However, some nodes occasionally require a different connection: Satellite Links with Geosynchronous orbit halve the Response of a hacker (minimum 1). Beam Links require direct line of sight, and are affected by rain, fog, and clouds if they use a laser. Microwaves can also be used with no environmental considerations.
AR / VR
This is no difference between what you can do with AR / VR. However, VR has bonuses / penalties: In cold sim, you use your Matrix initiative, and receive an extra initiative pass. However, you also take a -6 penalty to any physical action.
With Hot Sim, then you have two extra initiative passes, and get +1 to your matrix initiative. You also get +2 to all matrix tests. However, the -6 to physical tasks is still there.
Generally, if you need to interact with the physical world, use AR. If you can avoid that, then use VR.