F9 what does it do?

Hello Davyboy

The F9 key is for the in-game area protection mode.

Its best to be in creative mode, either start a new game and set it as "creative" or you can go into creative by pressing the tilde key ` and typing GM 1 (GM 0) will turn it back off.

Press F9 and click n hold your left mouse button and drag it around the area that you would like to protect ( Red box ) you can change the size by the pageup / pagedown keys and also by the arrow keys.

Once you have covered the area that you need, click and hold your right mouse button that will create the area for you, once done you can now press 2 this is the area edit mode.

Make sure the area is green ( just move outside and look at the area that you have just created) now press and hold your right mouse button, this will bring up a sub menu with which you can add a name to your area plus other things.

I haven't played this for a while but as far as I remember this is all correct.

What it does is well explained by Groovaholic ... however, it's not needed in a single-player game.

The areas are mainly intended to protect a player's buildings against access (destruction; theft of items) by other players.