If you have a Red Hat CDROM, select "Local CDROM" as your Installation Method. The other installation methods require more preparation-chances are, if you are using one of these alternate methods there is somebody that can help you.
At this point, the system may prompt you for the Supplimental Disk. Insert it and acknowledge the prompt.
Unless you are already running an older version of Red Hat Linux, select "Install" when presented with the option to Install or Upgrade.
Unless you are sure that you want to use the "Workstation" or "Server" installation class, select "Custom". The "Custom" installation class gives you the highest level of control over what packages get installed, and is the best choice for systems with limited disk space.
If you don't know if you have any SCSI adapters, you probably don't. Answer "Yes" or "No" as is appropriate for your system.