In the olden days, websites used to have a nice little symbol that would line you to their RSS feed. I don't know why they don't any more. But some good guys still do. Take for instance the BBC News site. You have to look for it, but about halfway down the right-hand column, in the Follow Us section, right under Facebook and Twitter is the RSS icon labeled RSS News Feed. Click that and the url it takes you to is what you need.
The good news is, almost everything generates RSS: blogs, forums, news sites, a lot of social sharing sites, so there's plenty of them to choose from
The bad news is, you may have to dig a bit to find the actual feed. But don't worry, we'll walk you through it.
First, go to the web page you want to look for an RSS feed on. For example go to http://ma.tt the home blog of Matt Mullenweg, the founder of WordPress. There's no happy little RSS icon to be found.
Second, in your browser, find a menu item that says "view page source". This will show you the HTML that makes up the page. On Firefox, you can just hit Control-U.
Third, look for "RSS". In Firefox, this is done by typing Control-F for find and typing in "RSS" into the search box. One of the first things you'll see is a line that includes href="/https://ma.tt/feed/". That's what we need.
And there you go. It's very typical for WordPress blogs to have the feed at BlogURL/feed. Try this on various other sites. More likely than not, there will be an RSS feed available. As far as YouTube goes, that's a bit more complicated.