Along the top of the screen is the Menu Bar. Each word represents a different menu of PowerPoint commands.
If a command is also on the toolbar, then the toolbar icon appears alongside the command. Some commands will also feature the keyboard shortcut.
Commands that appear ghosted are unavailable for use.
The menus can be customised to show full menus. If they do not, then you will notice a pair of chevrons at the bottom of the menu, and the full menu will appear after a short delay.
To show the full menu, click Customise under the Tools menu and check the option to Always show full menus
When you right click on the screen a shortcut menu is displayed. These contain a list of commands relevant to the object you right clicked on.