Your Spanli web address
Every site gets an address of its own, set up for you the first time you publish. You never have to buy a domain name to be online.
Your site does not need you to buy a domain name before it can go online. It gets a web address of its own - a real link you can send to anyone - the first time you publish, which is included with every paid plan.
Before you publish
While you are building, your site runs in front of you - the real thing, not a mock-up - at a preview address. It is not listed in search results, so a half-finished page will not turn up when someone looks for you. Treat the preview link itself as shareable-if-you-send-it: anyone you give it to can open it, so it is fine for showing a colleague and not a place for anything private.
Building and previewing are free, for as long as you like.
When you publish
The first time you publish, your address is set up for you automatically. Nothing to choose and nothing to configure. Publishing is what puts a site in front of the public, and it comes with a plan - so the address arrives with your first publish.
You will find it in your project's settings, under Domains, listed first as the site's main address. That is the link to put in your social profiles, send to customers, and print on a card if you are in a hurry.
Visitors reach it over a secure connection - the padlock is set up for you and you never see a certificate.
It is a real address
It works everywhere a web address works: shared in a message, opened on a phone, found by a search engine, linked from your social pages.
The only thing it does not do is carry your name - it is an address Spanli gives you rather than one you own. For most people that is perfectly fine for the first weeks or months, and some sites never need anything else.
When you get your own name
Buying or connecting your own domain does not take your Spanli address away. Both keep working, so links you already gave people keep landing on your site.
See Using your own name.
Changing it
The Spanli address is derived from your project's name and is not something you can rename afterwards. If you need a different address, that is what your own domain is for - and it is the better answer anyway, because that one is yours.