A Few Questions about ATC

I'm still learning about OpenBVE, and I'm wondering if someone might be able to help with a few questions about ATC.

First, is the availability of using ATC a function of the route, the train, or both?  In other words, does a route have to be configured/programmed for ATC, does a train have to be configured/programmed for ATC, or do routes and trains both have to be configured for ATC in order to use it?

In OpenBVE, how can you determine whether  a train/route is ATC capable?

Finally, how do you activate/disable ATC in OpenBVE, assuming that you're using an ATC-compatible route or train?

Thanks!

First a note:
I very strongly suspect that you're confusing ATC with safety system plugins in general. This post is written with that in mind

Unfortunately, safety systems are a wide and varied topic. The only real hard and fast rule, is that a train / route combination designed to work together will do so!
Other than that, the majority of stuff set within a country's geographic area will tend to be cross-compatible, so for example, most British trains will work correctly on British routes, Japanese trains on Japanese routes and so-on.

In-game, safety systems don't need to be activated as such, they're just 'there'. When the train passes over a beacon set by the route developer (or via time based conditions etc.), the plugin may choose to take an action, which might include modifying the power handle setting, lighting a light etc.

ATC itself is a Japanese safety system. This was included by default in BVE1 / BVE2 trains, and some basic instructions for this may be found here:
http://openbve-project.net/play-japanese/

If you need instructions for a safety-system plugin, then you really need to look in the manual or on the download page for the train in question.
Many trains will also have a basic quick-reference sheet if you scroll the panel to the right.

Please also note that many safety system plugins are Windows only. You'll be able to see this if a message pops up in the top-left of the screen after the game loads.
In this case, you'll find that many features of the train you're trying to use will not work; There's nothing to be done about this at present.

The acronyms "ATC"/"ATP" (automatic train control/automatic train protection) seem to be used for safety systems in general in the industry, though I'm not 100% sure, I'm seldomly reading papers in English. In German "ZugBeSy" (Zugbeeinflussungssystem, literally train control system) is usually used.

The availiability of built-in ATC is set by enabling it in .Sta, so it can be availiable on per-station basis only (you can tell ATC sections by looking at the line map before starting the game on the Map tab, sections where ATC will be red instead of black), and train uses ATC parameter in train.dat. But plugins can implement various ATC systems (there's plenty in Japan alone, some like WS-ATC are even closer to builtin ATS-P rather than ATC), some (like Usao's plugin for Tokyo Metro, Tokyu, Tobu and Seibu trains) require a start-up procedure (actually, the startup sequence depends on the route used, even with route/train designed for each other, as per reality) and won't take route beacons designed for other systems. But trains of the same company will most likely work well interchangeably on the same route.