"what happens to all my personal documents etc if i log in from the work account?"
They are in your personal accounts user folder, which the work account shouldn't be able to access.
"will i be able to access my stuff with a password or something, or will i have to log out and log in to personal again?"
Log out and log in as personal, or just do a switch user and both accounts can be logged in at the same time, then you can switch between them fairly quickly.
"will the people have access to all programs etc? "
Generally, yes, although some programs give you an option when you install them to either install for all users or just current user, if you've installed any for just the current user then other users won't be able to access them.
"is there a guide to this anywhere, so i can adjust settings etc? "
What settings? the only real settings are the account type, generally either normal user or administrator, don't set the work account as an administrator otherwise they'll be able to access all your documents.