Wow, hit random keys much? Looking at the menus, I see that f9 sorts the lines in file (under the edit menu). As long as you haven't saved the file in this state, there are 2 ways to proceed.
1. Undo (ctrl+z by default, under the edit menu)
2. Close the file without saving and re-open it.
The reason why there is no tutorial covering this topic is because Undo is a feature common to just about every application used to edit text in one way or another. From Word Processors to spreadsheets to text boxes in browsers, if you hit ctrl+z, chances are it will undo the most recent edit. Undo functionality has been a part of programs for 20+ years. It's assumed that if you are using a programmers text editor that you are familiar with the basics of editing text on a computer.
For more advanced topics, you should know that most of the support for Sublime Text comes from the community. But, the most basic way to learn keyboard shortcuts for things in any editor is to simply take the time to go through the menus of the application. That is how I determined what f9 did, and trying it out, I noticed that it put my window in a "dirty" state, meaning that the contents of the window had been changed, but not saved. This is indicated by the "x" in the buffer tab being replaced by a filled in circle. In general, if an action does this, it can be undone with the undo function.
For basic editing, you probably just want to stick with the things that are in the file, edit, and find menus. Once you are comfortable with most of the topics in those menus, move on to the selection menu.