How to put up a holding page while you build
A simple page that says something is coming, uploaded once and left alone while the real site gets built behind it.
A holding page is a single simple page shown at a domain while the real website is still being built behind the scenes — usually just a logo, a short message and perhaps a contact address, uploaded once and left alone. It exists so a domain does not sit blank or show a server's default page while work continues.
Creating one
A holding page needs almost nothing: a single index.html file uploaded to the root of public_html is enough, since that is the file the server looks for by default. It does not need a database, a content management system, or anything beyond basic HTML — the simpler it is, the less there is to go wrong while you are focused on building the real site elsewhere.
If you are developing the real site on the same hosting account, build it in a separate folder or subdomain rather than directly inside public_html, so the holding page keeps showing correctly at the domain until you are ready to switch it over. Previewing a site before changing DNS covers testing the real site without disturbing what visitors currently see.
Keep it out of search results while it is a placeholder
A holding page with almost no content is not something you want ranking in search results in place of the finished site later. Add a noindex meta tag to the page, or a rule in the site's robots.txt file, so search engines note the domain exists without indexing an empty placeholder as its permanent content. Remove that restriction once the real site replaces it.
Holding page vs maintenance mode
A holding page is normally for a brand new domain that has never had a real site yet. If you instead need to temporarily take an existing, already-indexed site offline for maintenance without harming its search standing, that is a slightly different situation with its own correct approach — see putting a site into maintenance mode, which uses a proper server response code rather than a plain placeholder page.
Replacing it once the real site is ready
When the actual site is finished, upload it into public_html in place of the holding page, or switch the domain to point at wherever you built it. Uploading your first website covers that final step in full once you are ready to make the switch.
Related reading
Two ways to check a site works before a domain change goes live, so the domain switch is the last step rather than the first.
How to upload your first websiteTwo ways to get your files onto your hosting account, which folder they belong in, and how to tell the upload actually worked.
How to put a site into maintenance modeA holding page tells visitors you are working on it, rather than leaving them staring at a half-finished change or an error mid-update.
Do I need both a domain and hosting?Yes. A domain is an address; hosting is what the address points to. A website needs both before it can go live.