Once you have your Drupal site up and running, it's a good idea to create a subdomain that can allow you and a team of developers to work on a website at once without mucking around too much with the site that is in production and already getting traffic. One of the best ways to do this is to create a subdomain. Something like development.yourname.com. This can be easily done from your host's control panel which will typically have a big button that says "subdomain". From there you pull down your production site from the server to your hard drive and then copy it to the development site so that you have a mirror of the original site. Now you have a place where you can install new modules, try new themes, fix different pieces of code, etc. All of which can be done without harming any of the traffic you have in production as this environment can be closed off to people with no knowledge or the URL or access to that domain. When you are ready to go live you can either point the name servers to the new environment or move the files into production. Once the files are moved, the development and production environments should be mirrored again so you can work again on improving your website.