Arrow Keys to change the selected item.
Shift will work with the arrow keys to select multiple items.
Enter to open selected items.
The Windows key to open the start menu.
Alt will select menus like File, Edit, etc. Use the arrow keys to open those menus and change the selected menu/command.
Tab to change the button/control selected in dialog boxes and web pages (also selects links in web pages)
For shortcut buttons, search the relevant program's internal help for "Keyboard Shortcuts"
Probably the best thing for you to do right now is to (somehow) open up System Preferences, (Apple menu, or Macintosh HD->Applications->System Preferences) and then from the Accessbilities icon, go to Mouse & Trackpad. Then, enable Mouse Keys. This will allow you to use your number pad to move the mouse when the NumLock key is not activated.