After you have installed Drupal and created first user account (will considered as administrator/super admin by drupal system) then you have to configure few things.
Click on the menu item that says "Administer", its on your left sidebar. That will lead you the the Drupal admin screen. You will find some menus: Administrer, Content management, Site building, Site configuration, User management, Reports and Help.
There are some basic security configuration you should to know before you create content and publish your site to the world.
1. Home -- Administrer -- User management -- User settings
By default drupal site will choose "Visitors can create accounts and no administrator approval is required." for you. Change