Choosing a domain name can be tricky. You might have a great one in mind, but then you check and someone else has already registered it!
If you really wanted to register www.smoove.com, you'd enter "smoove" in the top field and hit "Check". For another TLD, select "com.au" in the form and see if www.smoove.com.au is available. If it is, then the form will auto-populate that choice.
If you've already registered a domain name (or even already have a website) then you can enter your domain name in the "Proposed Domain Name" field (provided you've purchased a package that supports it). Otherwise, you'll have to select a domain name that's available so that we can register it for you.