There are two kinds of pages: public and private.
Anyone with a link to a public page can access it. Private pages can only be accessed by members of the workspace the page is in.
⚠️ Note: images uploaded to a page have direct links that are accessible even if the page is private. We plan to change this. If you'd like it to happen sooner, please comment at this roadmap entry: Hide images behind auth.
There isn't a catalog of public Brick pages. The only way somebody can find a page is if you share its public link with somebody.
When you share a page with somebody, they will see its children and its parents until the top-level page. They will not see other top-level pages. From this point of view, every top-level page is like a small anonymous website, independent from all the others.
One of the founding ideas of Brick is that pages are anonymous by default and can not be traced back to their owner. It is also impossible to figure out if two different pages belong to the same account or not.
Google only indexes pages that were explicitly submitted to the index, or pages that are linked to from other public pages on the internet.
Google does not index pages merely because they were opened in Google Chrome (or sent via Gmail, or shared in a messenger app). So, your pages will not appear in the index if they are not linked from other pages on the internet.