> But will be less logged now adding the -s option?

No

> What consequenses will it have?

cf man syslogd. You don't want -s if you want another computer to send
its syslog output to your computer.

> In general...........
> What is logged all? I mean, when ppl try to scan my machine with
> nmap...... will that be logged? And if not.. how can i log that?

cf man ipf and ipmon -s to log particular ports.

> I want all actions from outside logged if possible.
> FOr example if just a user logs in on my machine, i want a message on my
> screen that that and that user logged on.
> That only happens when someone tries to be root on your machine and stuff
> like that. Then you get messages on your screen.
> But is it possible that from any action from outside you'll get messages
> on your screen or begin logged?
> In what log files is can i find what?

cf man syslog.conf - actually take a look at your /etc/syslog.conf file!

Cheers,

Patrick