Where are you getting the link from? Are you getting it from the address bar above the web page?
For your Interesting Adventures of Emily. P the address looks like this if you are on the page: https://forums.theaetherlight.com/t/the-interesting-adventures-of-emily-p/1492
If you are looking at the 55th post in that thread you can click the ... next to the like button on the post and it will open up, there will also be a sort of chain there which will give you a link directly to that post, when I do click the button the link looks like this: https://forums.theaetherlight.com/t/the-interesting-adventures-of-emily-p/1492/31?u=goku_ironheart
Try again and I'll try help you figure this out
You can highlight words in your post, you usually want ones that are related to the link, and if you click the chain button right next to the " or quotation marks just above the reply text box you can add a link to those words. Feel free to try here.
If it still doesn't make sense Hanna made a step by step on how to do it just above.