You have several options for creating custom pages. The first is to create  a
Basic web  Page, which is a SharePoint page  shell that you can add  content to
using the built-in Rich Text Editor. This is stored in a web page directory
under your current site. For a page of text, links, and simple components
such as images or tables, this is the easiest approach. You then put a link
to the page in your team site.

If you want a page with web part  zones, but just want to change the layout,
you can create a web part page. There are several layouts that you can
choose from, and these pages are also stored in the same subdirectory. (OK,
you and I know they aren't really subdirectories, but that's what they look
like in the address bar). You could use this type of page with a Page Viewer
Web Part, for example. Again, you can link  to this page from your site.

These pages have the site  banner with Search, top Nav (tab) bar, and
breadcrumbs, but no Quick Launch area.

The third option is to create a custom page through programming, but this is
quite complex, and there are books and courses written on that. I'll let the
list experts field that one!