This is a much tougher question than you'd think. You don't subscribe to "Roku streaming" (unless you fall victim to a scam). Roku itself is free and doesn't offer any kind of subscription. They do, however, provide a payment method (Roku pay) where you can pay through them for any number of "premium" services (e.g., Paramount+, Peacock, Max, etc.), but most here would advise against subscribing to anything through any third party like Roku, Amazon, Apple, etc.
Lots of people are confused about what "Roku" is. Roku makes little computer boxes that connect to your TV and run apps. The vast majority of those apps are created by third parties that are solely responsible for the content and function of those apps. Most apps are free to add, but may require a subscription to actually watch anything. There are quite a few that are completely free supported by a plethora of ads.
More and more "The Roku Channel" has become synonymous with "Roku service". It's just another app, but many people probably use it exclusively since it has so much content that is mostly free (ad supported). You can also subscribe to "premium" content that is accessed through that app. It has "live" channels and a guide. Most of those "live" channels show old reruns 24/7 and the same ads over and over again. There are a few live news channels, but it's not the same as what you'd get via an antenna or cable.
There really is no way to get your local channels for free with just a Roku device. You either need a paid streaming service that provides those channels or another tuner device (e.g., Tablo or HDHomeRun) that you access with, you guessed it, an app. Basically, if you're using an antenna now connected to your TV to get your local channels you'd still use it after adding a Roku device.
Fox News has an app, but you won't get access to the live cable channel if you don't have it as part of cable, satellite, or streaming package. You'll just have access to clips. There are several other apps that are similar. Whatever sports you want will probably cost money and/or require a cable/satellite/streaming package.
By the way, Roku originally called their apps "channels" just to cause confusion with cable customers (in my opinion). They still can't decide if they're "channels", "apps", or "plugins", so you may see them referred to as any one of those. I'm sticking with "apps" and reserving the term "channels" for content within an app.
If you're used to cable, Roku isn't a drop-in replacement and if you thought you were going to get everything you had for free (or even cheaper), that simply isn't the case. You can easily pay as much for separate subscriptions to various services that you were paying for cable.
The channels available within "The Roku Channel" are constantly changing. @AvsGunnar does his best to try to keep up with it. You can see the list he compiled here. You probably won't recognize most of them since they aren't traditional cable/TV channels and you won't see any networks there.
You may just want to get a device and try it out, but remember, Roku is free! There's no cost to set it up and no cost to try it out.
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