If you're surfing the web, and see a page, or a video, or a blog (like this one!) that you would like to share it on your Google+ page, simply copy the URL (that's the address there at the top of your browser which looks like this
No, don't try to type it, you gotta use copy and paste. And once you've copied it, go to your Google+ page and start writing a post just like you always do. And say a little bit about why you're posting it, such as "Great advice here about Google+! I always wanted to know how to add a link!". You don't need to add a bunch of nonsense like "click here" or "You'll love it", just a short description is best.
Since Google+ updated its interface in November of 2015, the link icon has gotten even more vague. Originally, it was supposed to look like a paper clip, but now, well, I'm not sure? What do you think?
Anyway, when you click on that strange little icon, a box opens up that says "Add a link". It would be nice if the icon said that, but hey, nobody asks me. I'm sure they mean well.