Here are step by step instructions for some of the most common problems that I've run into, especially, for new Internet users
Networking with System 8 and up.
Including iMac, G3, G4, and iBook
"Classic" Networking (MacTCP) vs. Open Transport: Which should you be using?
How to set up "Classic networking (MacTCP)
Open Transport Networking Using FreePPP
Open Transport Networking Using OT/PPP