What is the "action" name for opening a file in the main menu, up top- "File" (the F is underlined? Most of the other files up here have the first letter underlined. Is there a short cut for opening those that do?
If I got your question, it is simply Alt+F (the letter underlined).
But to open files I normally open Ctrl+Shift+N - this is actually my most used shortcut.
IntelliJ IDEA and all other Jetbrains IDEs are highly customizable and have shortcuts for pretty much everything. It is worth to download a cheat sheet, study, and if you are still not satisfied explore the customization (you can also save to use it on other PCs).
Gustavo, you have sorted my query out very nicely; thanks;
Since i have rebound all the Alt- shortcuts which could open a menu item, i can't discover (not in File>Settings>Keymap, or even on the cheat sheet) the name of the "action" which would permit me to rebind an existing shortcut (eg. for me Ctrl-F, would do to open the File item);
In the future, you really should ask JetBrains support questions like this. They'd be better-equipped to help. It's a bit off-topic here.