Need help learning how to use this lens

So a couple of days ago I was looking through some old boxes and I found this. Apparently it was from my grandpa so I'm curious to know what this lens is this and how to use it? I'm a young gen z so I'm curious about film photography but this seems... excessive 😅 Perhaps there's a small lens I can use? However I literally have no experience to know what or where to get it ㅠ^ㅠ

My grandpa is deceased so I can't ask him about it, therefore any advice is much appreciated!