If you want to develop a new website but you don't want to affect your existing website (e.g you cant transfer your domain yet because you want your existing site to stay live while you develop). There are a couple of ways to do this:
1) Is to login to your WordPress database and change your Site URL. However, when you launch your site, you may end up with some broken links.
2) What I will show you in the video below, is edit your host file on your computer so that when you type your URL it will point to the location where you are developing your site. The downside is that you need to do this on any computer where you wish to view or work on your site but this isn't usually much of a problem.
I recorded this video because I was removing entries from my host file but here is the entry that you need to add to your host file.
The first part is the IP address that your hosting company will provide, then a space, then your domain without www. and then a space and then your domain with the www.
220.127.116.11/~username/ example.com.au www.example.com.au
First I show you where the host file is located and then I run notepad as an administrator so that we can edit the file.
This is done on a PC, on a mac the file is located at (and I dont think you need to run notepad as administrator first) /private/etc/hosts
You may need to clear your cache before you can properly resolve the domain to the new IP.
Feel free to ask me if you have any questions.