Changing where a page appears in the main menu or dropdown menus of your WordPress website is controlled from the Appearence > Menus section of the dashboard.

Adding a page to the menu

From the menu editor area of the dashboard you simply tick the page you want to add to the menus. It then appears at the bottom of the list of pages (you may have to scroll down to see it) and from there you can drag it into position as you wish.

You can remove the menu buttons using the Remove link which is visible when you click on them. If you have a really long menu dragging the button to the top can be tedious but you can click on the link which says To the top which then places that menu button all the way at the top of the list.

Rearranging the menu is done by dragging the items

Each link in the menu that is a top level item, usually the links immediately visible on the menu bar of your website are the buttons aligned to the left. If there are sub menus, typically drop downs, then they will be indented. Multiple items indented one level deep will create a multi item drop down menu. You can continue to indent to additional menu levels but it becomes clumsy for the person browsing your website.