1. tset is a program used to set the TERM variable and various stty modes to initialize the users tty environment. I don't like the program and prefer to simply set my TERM variable and use stty as required. The -s makes it output shell commands. The first tset, which is invoked if TERM is not set, will ask the user to enter the terminal type and offer "hp" as a default. The program will then print "TERM=hp ; export TERM" or something very similiar. You can just type the command and observe the results. But this is done inside an eval ` ` construct. Eval is a shell built-in that evaluates its arguments and then executes the resulting command. Type
eval `echo date`
and maybe it will make sense.

2 "nobody" was introduced along with nfs. It's an anomymous user used in nfs security. A process can be given the uid "nobody" which then only allows it to access world readable programs. "noaccess" is similiar, but for files. No process should ever have the uid of noaccess.

3 nis or nis+ perhaps.

4 Now really. Add a line like "echo in .login" to each file and observe the results as you login.