Good to see you recruit! Here you can find the basic manual that comes with the game, BUT before you start your heroic campaign in ArmA III please read through the following information, then once you have fired up the game you should move onto basic training which can be selected when you first log in:
There is also the link below to the Keyboard layout that you can use for reference:
Below is a screen shot of the 'DEFUALT' keyboard layout:
Below are some relevant pages from the manual to get you started
Hang tuff, stay frosty and keep up the good fight!!