Q: What is a launch option?
A: Launch options are commands, that let you tell the game to perform an action when launching it or that let you force a specific setting. For example, you can specify a window height and a width you want the game to start with. Every new launch option starts with a dash, but you can also put console commands in the launch options. These need a plus in front of them (e.g. +exec randomconfigfile).

Q: Where can I set these launch options?
A: Thats rather easy. Take a look at the picture (You can find it at the end of the guide) and just follow step by step:
launchoptions1. Right-click Counter-Strike: Global Offensive in your game library in the main Steam window
2. Select Properties in the menu
3. A new window will open. Click on the SET LAUNCH OPTIONS button
4. Another new window will open. In this one, you can set the different launch options. Every new launch option starts with a dash or a plus, DO NOT separate the launch options with a comma or a semicolon, just a space needs to go in between the different launch options.
5. Click OK and Close and your all set!

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THIS WILL CHANGE YOUR RESOLUTION YOU HAVE BEEN WARNED!

Launch Option to get a good 50 fps boost!:
-w 1024 -h 768 -freq 144 -refresh 144 -processheap -novid -nojoy -noforcemparms -noforcemaccel -high -tickrate 128 -threads 4 -nod3d9ex -noaafonts +mat_queue_mode 2 +exec autoexec +mat_vignette_enable 0

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Hope this helps.