Logitech Gaming Software (LGS) comes with support for hundreds of games built in. When you first run the software, it should scan and automatically set up game profiles for you. If you install more games later, you can rescan for supported games and have profiles imported for them.
To scan for supported games and import pre-made profiles:
Open the Logitech Gaming Software:
Start > All Programs > Logitech > Logitech Gaming Software 8.x
Click the glowing G-Keys.
Move the cursor over the "+" icon in Profiles and look for the down arrow to appear.
Click the down arrow under the "+" and click "Scan For New Games".
A pop-up window will display while the software scans for games. All detected games will be visible at the top of the list with a check mark next to them. Newly detected games will be highlighted in teal. These games will have profiles added to your system when you click OK.
NOTE: To add a profile to a game that wasn't detected, find the game that's highlighted in white in the list and select the check box next to it.
Click OK. The software will automatically import the profiles for the newly detected games, and for any game you've selected manually.
NOTE: For any games you've selected manually, make sure to edit the newly created profile so the correct game .exe file is assigned to it. To manually assign the game .exe, see answer 360023406853.