It depends on your real purpose, what you mean by "accessible to the world ... or something." If you want it to be constantly accessible from the Internet, you need to place it on the server (whether it is shared or dedicated), you wonโt keep your Mac turned on forever, right? :)
To host Django on shared hosting - I would recommend webfaction, step-by-step guides for setting up a Django project can be found in their scripts and forums ($ 9.50 per month for a basic plan, with a two-month money back guarantee, which actually works, I tried it myself :) . Additional Options at Djangofriendly.com
For a dedicated server, ask yourself if you prefer to manage the entire server (OS, web server, database server, memcache, firewall, backups ...) yourself. If the answer is yes, check out Linode , Rackspace or Slicehost or even amazon web services , but keep in mind that this is more expensive, it is more complicated, but it gives you ultimate flexibility. When you are ready to try, this is one of the best lessons I have found on the net for this subject .
If all you need is proof of the concept that โeverything I can get from my web browser should be accessible from anywhere in the world,โ ask your Internet provider if you are provided with a private iPaddress. If not, hmm, better go for the options mentioned above :) If so, find out what IP it is by visiting whatismyipaddress.com . Then start the web server as suggested by Prashant and enter the IP address from whatismyip.org in your browser. Get nothing? a) disable the MacOSx firewall. nothing yet? b) connect the Mac directly to the network cable provided by your provider, without a router between them. Re-enter your IP address in the browser. Works? excellent, go to google port forwarding, it will say that you need to configure the router for the same effect when using the router. Is not it? Ask a separate question in stackoverflow and provide as much information as possible about what you are doing as you can.
Sharing Mac os is not practical if the packages are not routed correctly to access your computer on the network. I think all he can do is start apache and open some ports in the firewall. But if your personal router or Internet service provider does not forward external packets to your computer, you will not get what you want.
Good luck