So, you want to learn about RSS. You are in the right place, not because I'm an expert or something, but because I did some research XD. First of all:
What is RSS?
(Before you go ahead, there's an extensive and detailed explanation in ResearchBuzz, written by Tara Calishain. I'll try to be a little more brief). You can find a lot of explanations of the achronym, but the most used one is Really Simple Syndication. Nowadays, the main use for RSS is for podcasts. Years ago, Google had a product that made it easy to use RSS, but Google likes to kill lot of it's products for a variety of reasons, and Google Reader went down in 2013. I never used it, to be clear. I'm fairly new to RSS, and I only found out about it because I started building this website. RSS is basicaly a way to syndicate or publish content so that people that subscribe to it don't have to check the main source periodically. What does this mean? In the case of podcasts, users that subscribe to it are notified whenever a new episode comes out. In the case of news publishers or websites, subscribers can see when individual articles get published instead of having to check the site periodically. Also, you can use it to group all the sources you want to subscribe to in one place, and because of how it works nowadays, if used correctly by the publisher, you only get the content of the article, without any bloat from ads, navigation elements, etc. Sounds good, right? Let's get into it a bit further, both from a consumer and a producer perspective.
How do I use it?
First of all, you'll need a feed reader. There's a lot of both paid and free options, even some browsers like Opera or Firefox have built in ones (at least at the time of writing). I personally recomend Inoreader. It's free (with a limited but generous number of feeds), multi‐platform, it has many quality of life features, like automatically finding feeds, and the paid version has features for filtering articles or note taking, for example. The article mentioned before discusses more options.
Okay, now you have decided on a reader, let's find out how you can subscribe to feeds. Some readers do it for you, like I mentioned before, but they are not perfect. If the site author is nice (like me XD), there will be a symbol that looks something like this: 
If that's the case, you're in luck! Click it and you'll probably get a page ending in .xml (if you click the one I provided you'll get my feed as an example). That's the URL or link to the feed, provide it to your reader of choice and you are done, you'll get new articles when they are added. There's a possibility that instead of opening a page, your browser downloads a file, also ending in .xml. Woops! If you know how to inspect a page, do that and find the href attribute, if you don't, keep reading.
If you weren't succesful by now, know that this is not your fault, the site is making it difficult for you (or your browser is a bit goofy). A variety of methods are discussed in the ResearchBuzz article I mentioned before, but I will show you the most effective ones. First, the browser extension route. There's a variety of extensions that try to find the feeds automatically, like this one. They are your best bet, usually, but let's say you can't or don't want to use extensions. Then there's some patterns you can exploit. For example, usually Wordpress based sites (wich are numerous) hide their automatically generated RSS feeds on /feed/. For example, let's say this was a Wordpress site (which it's not) and you wanted to get the feed for it. Then you'd go to https://kbs-lucas.neocities.org/feed/ and try your luck (there's some more of these patterns in the ResearchBuzz article). If none of these methods worked, the page might not have an RSS feed, sadly :_( Speaking of which, if you have a website, you wouldn't want to disappoint possible readers by not having a feed, right? Don't worry, it's not too difficult:
How do I make a feed?
As always, there won't be a better feed than the one you make by hand, understanding each item. It's not too dificult! The RSS's Board has the full specification, it's not too long and it's well explained. They also have a validator and a section that explains how to make your feed discoverable automatically (by extensions or feed readers, for example).
Too much work? I made an online tool that let's you make a feed automatically, just by filling out a form. It's WIP but I'm trying to make it foolproof, you can even validate the feed you are working on via the previously mentioned validator in just one click! If you compare what it produces with what my own feed looks like, you'll see that it's nearly identical, and that's not by chance! I mainly tried to automate the process of updating my feed for myself, and just expanded to make it accesible to everyone. It follows the RSS Board's specifications and recommendations (mostly, as I said it's still WIP but it's like 95% done, and usable right now). Feel free to use it and make suggestions about it via any of my socials. You'll still need to make your feed discoverable automatically (it's just a link tag in your homepage, after all), and I'd suggest making a link or a button to your feed also, like this one.
Happy syndicating!