What's correct? Keyboard, mouse/menu, or right-click commands

They are all correct!  That is the beauty of using a PC.  Either way is correct.  Sometimes a mouse is more convenient.  When doing repetitive stuff, like entering data into a checkbook register, it is easy to learn the few keystrokes needed to toggle between the data fields and makes the job go faster.  Sometimes a tool bar is not available in the window where you are working.  This happens when you are working on small bits of data like an address in an address book.  If you want to copy an email address but there is no edit button you can highlight it and press your "ctrl" button and then type "c".  Usually a right-click will do the same thing but if you accidentally erase that address, the edit menu might not display the undo command.  Simply press the "ctrl" button and type "z", the information will be restored (only the last action though so this is limited.)

All three ways are perfectly grand ways to use your computer.  Finding different ways to use the machine is a creative way to learn.