Hey this is quite the silly question, but is there a way to search for specific posts (images and videos) via its ID number? As sometimes when I get mail from users it always has a number next to the message which I assume is the ID of said post (unless that’s something else and I’m mistaking it).

That's more for posting. If you already had the ID number of a post then you wouldn't really have to search for it, anyway.

If someone sent you a post ID number rather than a simple link, just click on any other post then substitute the sent ID number for that post's number, hit refresh, and presto, there's the image or video you were looking for.