Many keyboards have a Windows key which will bring up the start menu. The keyboard combination Ctrl+Esc also brings up this menu. The up and down arrow keys allow you to move through the menu items. Those items with a submenu are visually indicated with a small black triangle/arrowhead. These submenus may also branch out further into other submenus. The Esc key allows you to go back one step in the navigation process. Once you have arrived at the desired item, pressing the Enter key acts in the same way as a left-mouse click to make a choice.
Another timesaver once the start menu is open is navigating by the first letter of the menu item. Pressing the “P” key takes you to the Program menu. If there are multiple menu items that begin with a particular letter, pressing that letter takes you to the first, top-most of those menu names. You can then navigate with the down-arrow.
Applications that have met the Microsoft Windows accessibility standards follow a standard menu scheme with headings like File, Edit, View, and so on. Combining the Alt key and the underlined letter in those menu headings will open that menu. Up and down arrow keys will move through those menus. Enter will pick a particular action.
The Open and Save dialogue boxes can be particularly intimidating to navigate by keyboard. The Tab key will navigate through the various fields. A Shift+Tab moves backwards in the navigation between those items. Once you have landed on an area within the dialogue box, you may need to use the up, down, left, or right arrows to make a more specific choice. Screen reading programs will read aloud the dialogue item you are currently focused on. Otherwise, Windows provides a visual cue of where the focus is. For a particular file name or dialogue button it will have a faintly visible dashed-line rectangle to around the item to show it has the current focus. Drop down menus are activated with the down arrow.
Forms can be navigated with the Tab key as well. Arrow keys allow the user to toggle between choices for items with a radio-button or checkbox. Once you have landed on the desired choice, the spacebar will make a selection. Pressing spacebar on an item with a checkbox selected will deselect the item.
For more information on keyboard shortcuts and navigation consult Microsofts' Keyboard Assistance and Shortcuts  web page.
-  Keyboard Assistance and Shortcuts