Open Question: Locked a file - can't find it, can't put on pw?

I was trying to lock/ hide one of the files the "My Pictures" folder on my computer that I didn't want everyone using the computer to have access to, but I may have done it wrong & now I can't find it. How can find it, how can I lock it (only that folder) without locking out the internet and everything else that the family might use? The way I hid it: I clicked on Properties (of the sub-folder) I want to hide. I changed it to "hidden," but now I don't know how how to find a hidden folder. Also, I don't know how/ where to put a password on it. (Which I guess I could do if I wanted to "unhide" it but still have access to it.) I was never given the option to add a password.