Before running pppconfig you should know what sort of authentication your isp requires, the username and password that they want you to use, and the phone number. If they require you to use chat authentication, you will also need to know the login and password prompts and any other prompts and responses required for login. If you can't get this information from your isp you could try dialing in with minicom and working through the procedure until you get the garbage that indicates that ppp has started on the other end.
pppconfig allows you to configure connections to multiple providers. For example, you might call your isp 'provider', your employer 'theoffice' and your university 'theschool'. Then you can connect to your isp with theschool'.
It can determine which serial port your modem is on, but the serial port must already be configured. This is normally done when installing Linux.
It can help you set your nameservers, or, if your ISP uses 'dynamic DNS', it can set up ppp to use that.
/etc/ppp/peers/provider is the standard pppd options file for the default service provider.
/etc/ppp/peers/ is the pppd options file for the provider that you have named __
/etc/ppp/peers/provider.bak is a backup copy of /etc/ppp/peers/provider.
/etc/chatscripts/provider is the standard chat script for the default service provider.
/etc/chatscripts/ is the chat script for the provider that you have named __
/etc/chatscripts/provider.bak is a backup copy of /etc/chatscripts/provider.
/etc/ppp/resolv is a directory where resolv.conf files for each provider are stored.
/etc/ppp/ip-up.d/0dns-up is a script that arranges for the correct resolv.conf file to be copied into place when a connection comes up.
/etc/ppp/ip-down.d/0dns-down is a script that arranges for the original resolv.conf file to be copied into place when a connection goes down.
/etc/init.d/dns-clean is a script that runs 0dns-down at bootup to clean up any mess left by a crash.