This all depends on where/ what program, you are trying to copy from, and where, or what program you are pasting into. If you can't simply highlight the text and then right-click for the copy & past commands, you may have to use your control functions. Use "Ctrl + c" to copy and "Ctrl + v" to paste.
Mike, I am trying to copy a section from an email on your program to a new email on your program. The right click menu with copy on it works on the email to be copied, but paste does not show up on the new email right click menu. Your control function suggestion does work, but ONLY if the new email is changed to plain text. I am accessing you through Firefox (AVG) as recommended. However, I just tried through Internet Explorer (Google) and the paste menu does appropriately drop down through that pathway - but reversed. The drop down paste functions only work on the HTML and HTML and Plain Text functions, but not on Plain Text! That is confusing since, when I try to sign in that way, I get a message that my browser is not supported and that I should use Firefox.