Dock app lost?

Total newb to this forum so please forgive the ignorance here. I was trying to reposition my dock like a dummy and did the old pc click and drag on error. However, I did not position the app back onto the dock and when i unnclicked thinking it would reposition itself in place, it vanished...just disappeared on me. Can I get this back on my dock?? how do I find which app it was that I lost?


Thanks!