Newbie firewall/masqarade/proxy confusion

[alandd@interwrx.com]

I confess to being a MS user for, low, many years.  I am now
coming into the Linux light!  It is making computer exciting
again.

I am scheduled to get DSL with a static IP in a week or 
two.  As a first Linux learning experience, I have setup an 
old 100MHz 486 PC, 32MB RAM, 1.5GB hard disk space, 2 16-bit 
Intel network cards, VGA, mouse, blah, blah... with RedHat 
6.2.  X still does not work but that is not important now.  
My intention is to have this little PC be a firewall for my 
other computers to share the DSL connection.

My confusion is this:  I am finding in my readings that what 
I thought was a firewall maybe something more.  I am still 
trying to understand the differences between the terms 
firewall, masqarading, routing and proxy server.  Maybe the 
confusion is from the fact that configuring TCP/IP is still 
a new thing to me along with Linux.

What I want to make is my Linux box providing a single 
\"presence\" to the internet while the workstations \"behind\" 
the Linux box can surf and do email without being \"visible\" 
to the internet.  What combination of 
firewall/masqarade/proxy stuff do I need?

Remember, I am a newbie, be kind.

Alan