vadfs

This may be a dumb question, but if I try to change the "privileges" on a restricted folder, like disk utility, and add a user to list of users with access to such folders, the users listed are me and "administrators." Is my mac just referring to all administrators on the computer or is there an actual account called administrators? I'm only asking because I'm the only user of the computer, so there shouldn't be any other accounts. There's also another account called guest account that I'm not sure about. Is that just an account that is on all macs? Also, this is unrelated, but do all macbook pro's come with the operating system installed? Because mine was brand new and it came with it on there. My old mac never did.

sinclair_tm

Rule number one, there is no need for you to change any privileges on your Mac, unless you are 100% you need to. The administrators account is really a group, which you are part of. If you take them off of a program, then you can't open the app. The admin group, as well as many others are, are part of the OS, and are needed for the computer to even run.
As for Macs, all new Macs come with the OS pre installed, and always have. If you got one without an OS, then that is very fishy.