For most new websites, you generally want a way of either completing a final preview or working on the site without affecting the current version of the website. Depending on your preferred workflow, there of ways you can upload and preview a new website using Plesk.
If you intend to develop the site on the server (rather than on your local workstation or separate development server), you can achive this by using a sub-domain of the main site (eg newsite.yourwebsite.com). Plesk allows you to create a subdomain easily (we have an easy guide here), where you can create a website (including a separate database) which doesn't affect the live site.
Once the new site is ready, this can be copied to the live site using the Plesk Website Copying tool. We have a guide specifc to WordPress here.
The Plesk Preview tool allows you to view your site without making any DNS changes. This is a great option when migrating websites to ensure it's working as expected. To preview your website, simply click on the Preview button within your website:
This will open a link based on the IP address rather than the domain.
For the most complete way to preview a site before it's live, you can edit your hosts file on your local workstation. This method essentially bypasses any external DNS and points direct to the IP address of where your development site is hosted.
Detailed Host file modification guide: https://www.howtogeek.com/howto/27350/beginner-geek-how-to-edit-your-hosts-file/