I was using Mac OS X 10.2 (Jaguar) before I became reasonably comfortable using the Terminal. In that version of the OS, the default Terminal shell was tcsh, and the default pager (a program called more) would let me open a man page and go into it as far as I wanted (or even reach the end), and then use the Terminal window scroll bars or page up and page down keys to navigate back up through the text that had already been displayed in the window.
When I upgraded to Panther (10.3), I discovered that the default shell was bash instead of tcsh, and a different pager (called less) was being used by default, so that only the man page text appearing at the moment in the Terminal window was available for viewing. Once it disappeared from the window, I had to use keyboard shortcuts like Control-D and Conrol-U to navigate down for later man text and up arrow for previous man text. Generally, I prefer to use keyboard shortcuts rather than mouse maneuvers if I can remember the shortcuts. In this case, though, they interfered with shortcuts I had already programmed into QuicKeys. Also I wanted the page up and down keys to work like they do in other applications, and if I reached the end of the man page or hit Control-U too many times and went past the beginning, I found that the man text was gone, and I would have to reissue the man command.
Anyway, here's how I added an alias for the man command so that a different pager would be used, and I could once again keep all the man text available in the Terminal window where it was loaded.
Open a Terminal window and check its title bar to be sure that the shell being used is bash (if you haven't customized the window title, it should contain "bash"). If bash isn't the default shell, you can change that in the Terminal preferences by selecting "Execute this command (specify complete path):" and typing in "/bin/bash". If you changed your shell, you should continue in a new Terminal window.
Next, type pico .profile into the Terminal window and press return. If you haven't previously customized your bash login options, you'll see "New file" at the bottom of the window when you enter the Pico text editor. Now type alias man="man -P more", and press Control-O to submit the changes. Type Y if prompted to confirm, followed by a carriage return to accept the file name. Then type Control-X to exit the Pico program.
Now open a new Terminal window to see the results. You might want to type in a man command that will result in displaying a manual entry with several pages, such as man ls or man bash.
[robg adds: There are some key differences between less and more, and people seem to prefer one or the other. A previous hint explains how to stop the less pager from clearing the screen, which helps a lot. Also, you can use the up and down arrows to scroll through documents that less is paging. Finally, you may already have a .bash_profile file in your home directory; if you do, add the above command to it instead of creating a new .profile file.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040914150552867