this preset adds ambient light, HDR, colour correction and removes blurriness of textures in order to make entities more clear in distance using sharpening algorithms.
Heads-up
first of all, You must be aware that Battleye will not allow you to use reshade (using it with battleye will not result in a ban, it's just block reshade from working) so basically you can't play with reshade on multiplayer server with battleye on.
Requirements
you need reshade, download from official website. link
How to Install
open reshade, click browse and navigate to arma gold edition directory, select arma.exe; then click next (skip the next window) and check the following reshade repositories :
1. FXShaders by luluco250
2. Legacy effects
3. SweetFX by CeeJay.dk (if it already isn't checked)
4. Standard effects
and click Next to download effects. place ReshadePreset.ini in arma directory where .exe is located.
now launch the game and wait for files to compile (this process happens everytime you launch the game). press Home key on your keyboard to open up reshade overlay.
on top, click on blue bar where it says "ReshadePreset", on drop-down look for ReshadePreset.ini. once you've selected it, the effects will apply to your game :D
Sidenote
since this preset contains ambient light and reshade preset applies on everything on screen including HUD and consequently makes UI much brighter than usual; therefore I recommend defining a hotkey to switch off and on reshade effects.
in order to do that, in game open reshade overlay (by pressing Home key), on top, go to the setting tab. on "Next to Preset key" simply define a key to for switching on and off reshade, (in my case it's "/" on keypad). now go back to Home tab, and click the plus sign next to blue bar. type a random name and tab enter. save the empty preset you've just created by clicking the floppy disk icon. now by the key you've defined you can switch off reshade effects whenever you are working in editor to get rid of shiny UI. :)