The good old Field Manual asks you to refer to the "keyboard overlay", which unfortunately is not included in the Steam version. Therefore you need to find out what happens when you press which buttons before you play the game. This guide will save you the trouble.

Also discussed here are solutions to game speed and sound issues, as well as control settings for the modern gamer.

Airborne Ranger is said to be the earliest example of the tactical shooter genre, back in 1987. It may seem old and awkward, but it is still a challenging and fun. I would be happy to help as many people as possible enjoy this game.

*I am not a native English speaker. If there are any poor points in the writing of this guide, that is the fault of the free translation tool, not mine.

The following information is taken from IGN's AirBorne Ranger : General FAQ. This article contains a lot of other useful information and is well worth reading.
https://www.ign.com/articles/2005/01/31/airborne-ranger-general-faq-583853

Arrow keys: Move
Keypad arrow keys: Move
Keypad 1,3,7,9 keys: Move diagonally
RETURN: Shoot
ENTER: Shoot
Keypad 5: Shoot
Space: Changes standing-crawling mode
1: Calls the aircraft earlier (decrease time to 10 seconds). Beware of this key, especially when you're playing with veteran ranger! If you accidently push it too early, it can ruin your whole career!
F1: Toggle Carbine (CAR-15 Colt Commando)
F2: Toggle Hand Grenade (M26)
F3: Toggle LAW Rocket (M72A2)
F4: Toggle Knife (M7 bayonet)
5: Toggle time bomb for 5 seconds
6: Toggle time bomb for 10 seconds
7: Toggle time bomb for 15 seconds
F9: Displays strategic map of area
F10: Sprint mode. The drawing of your weapon, and the background replaces its colours, when active. The sprint wears off sooner if you carry large amounts of ammo (see the "WEIGHT" when you press F9).
Pause: Pauses the game. Hit SPACE to continue.
Backspace: Use a Medkit (cures one critical wound)
V: Sound on-off
-: Decreases the game speed (for fast computers!) Press it only ONCE, because the second
press will slow down the game so much, you won't be able to get to the rendezvous place
in time (it doesn't slows the time down).

1. The game is too fast, so I recommend editing dosbox.conf in the game folder and reducing the "cycles" value. The default is 4000, but I play with it down to 2400. I also do not recommend using the in-game speed reduction keys.

2. As is evident in the title screen, the default settings do not play sound correctly.
I did not know how to solve this properly, but at least by changing the "machine" value in dosbox.conf to "tandy" and setting the game's graphics mode to Tandy-1000, the sound is played correctly. In this case, the game speed is even faster, so the cycles value needs to be reduced further. I play with it turned down to about 1200.

(Surprisingly, both game speed and sound remain broken in the trailer on the store page.)

1-1. In-game key configuration is not possible, but you can use the DOSBox mapper feature to some extent. You would want to use WASD to move your soldiers too, wouldn't you? First, start dosbox.exe in the Airborne Ranger\dosbox folder and press Ctrl+F1 to open the key mapper.

1-2. After setting up and saving, mapper-SVN.map will be created in AppData\Local\DOSBox. Put this map file in game folder, edit dosbox.conf and change the value of "mapperfile" to mapper-SVN.map. That's it.
Once you have the proper key assignments and start the game in Rotational mode, you can use WASD to play the game as if it were a modern game.

2-1. Or want to use a controller? Of course it is possible. I recently created a Steam controller layout for this game, hoping to be able to play it with a controller. In this case, not use the mapper-SVN.map described above, but will start working with the default key assignments.

2-2. First, you will need to do some complicated work to enable the Steam overlay in DOSbox. Fortunately, there is a very useful guide created by cammelspit. Follow this to get started.
https://steamproxy.net/sharedfiles/filedetails/?id=798840934
2-3. The downloaded DOSBox SVN Daum replaces the Airborne Ranger\dosbox. Don't forget to re-set the cycle in the saved dosbox.conf to the correct one, in this settings you may want to go slightly slower than the I wrote above. In the [autoexec] section at the end of the file, add the same settings as in the original dosbox.conf in the Airborne Ranger folder. Edit it as follows.
2-4. Next, rename RunGame.bat to RunGame.txt and open it in your editor. You will find the following line
To load the new conf file, change dosbox.conf to dosbox\dosbox.conf. Then rename the file back to RunGame.bat. Next, open win.conf in the Airborne Ranger folder and change the output value to the same as dosbox\dosbox.conf.

2-5. This should enable the Steam overlay. Find the controller layout "Airborne Ranger
test" I created in the community layout section and activate it.

Perhaps due to my error, an older, incomplete version may also appear in the list. Please select the most recent one.

2-6. Here is a preview of the layout

The main weapon keys are stored in a virtual radial menu set on the right stick. The rifle is equipped when the stick is tipped up, the grenade when tipped to the right, the rocket when tipped down, and the knife when tipped to the left.

The start button is assigned the keyboard key "2". This means that you press it to set Tandy mode when selecting the game mode and Directional mode when selecting the control method.

(Occasionally, you may not be able to change weapons. I think this is a bug in the game itself. I don't know how to deal with it at the moment.)

I wrote this in a hurry, so there may be some parts that are difficult to understand or not fully explained. If you have any questions, please feel free to ask.