I've been trying to post pictures and videos on my page but haven't figured out how to do it with the URL, is there anyway you can help me?

But how do I do it on URL?

For Youtube videos, remember to only copy the part after "watch=". So if, for example, you want to post this video, the URL of which is "https://www.youtube.com/watch?v=3pY0gZRb8kE", you just take the string of characters after "watch=" (which I highlighted), and then put it in the brackets, like so: [youtube=3pY0gZRb8kE]. Doing so will embed the video into whatever you're writing, like this:
[youtube=3pY0gZRb8kE]

[youtube=naeQt0vv_k0]