You may encounter tips, guides, or instructions that ask you to set registry keys for Windows applications. Each bottle has a separate registry and registry keys set in one bottle do not affect other bottles. The registry keys on a bottle only affect the programs in that individual bottle. This is another reason to install your applications into their own individual bottles.
There's a great breakdown of useful registry keys over at WineHQ. In this guide's example we'll demonstrate setting the useGLSL key to enabled.
To start, go to the Bottle menu and choose Run Command...
Type in the command regedit and click Run.
You've now opened the Registry Editor.
Browse to the location specified in the instructions you're following. Again, for this example we'll add useGLSL=enabled to HKEY_CURRENT_USER/Software/Wine/Direct3D which is a fairly common value to set for 3D games.
Please note it's fairly common to abbreviate HKEY_CURRENT_USER as HKCU, HKEY_CLASSES_ROOT as HKCR, as so on.
Browsing to HKEY_CURRENT_USER/Software/Wine we see that Direct3D isn't there yet.
To add Direct3D right-click on the Wine folder and select New>Key.
Rename the New Key entry that appears as Direct3D.
Next right-click on the new Direct3D folder and choose New>String Value. A new string key appears.
Change the name to useGLSL. Right-click the new key and pick Modify.
Type enabled in the Value data: field and press Ok.
That's it! You've now added the string Value useGLSL=enabled to the key location HKEY_CURRENT_USER/Software/Wine/Direct3D.
There's nothing you have to save, simply close regedit to make the changes take effect.