A fresh install of SPIP will terminate with a site that is essentially empty. First things first, start creating the layout of your site — at least one section is required. You can then add more sections later on when you want.
To create the first section, go to the private area, click on "Site edit" in the top banner, then click the "Create a section" button to create a new section or sub-section.
Enter the required data into the form.
And then continue to create new sections and sub-sections until you’ve finished creating the site hierarchy.
Read the next article: I have created a section but it isn’t displayed on the public site!