That all depends on how you have the site setup in IIS.
If the site is setup using Host Headers, you need to add the domain you are using in your site host header to your hosts file on your local computer with the IP 127.0.0.1. After doing this, you should be able to enter the URL in your browser and the site will come up.
Example hosts file:
If the site is not setup using host headers and only has an IP address assigned to it, you should be able to just enter the IP address of the site in your browser.
I suggest that if you are testing the site and you don't want to use it for your main site yet, that you setup a sub-domain (like dev.mycoolwebsite.com), point it to your server using DNS and setup that domain as a host header on the mojoPortal site in IIS. Once you have decided to switch to the new site, all you have to do is shutdown the old site and add the real domain (mycoolwebsite.com) to the host header of the new site. You will also want to make sure you direct DNS to the correct IP address.
There is a lot more that goes into configuring sites in IIS but this should get you started.