First of all you can read the article dedicated to the 3.5 version introducing cheat function (
http://www.gateway-3ds.com/gateway-ultra-v3-5-public-beta/), specially this part:
HOW TO USE CHEATS
=================
1. Simply copy the folder "cheats" into the root of your microSD card that will go into the Gateway RED card.
Each file inside the cheats folder will be of the format <TitleID>.txt where TitleID is the title id of the game.
2. Boot into Gateway mode, and press SELECT to make the Gateway game selection menu appear.
3. Select your game and then press Y to enter cheat mode.
4. Enable the cheats you want and then press START to load the game.
This is pretty explicit on where to put the files and how to activate the cheats.
The TitleID is the unique ID of the game, if you look into the existing cheats folder zipped with the last Gateway version, you can see some txt files named accordingly (i.e. 0004000000035400.txt where 0004000000035400 is the TitleID).
So now let's say you want to cheat on Ridge Racer 3D EUR :
1/ Go to
http://fort42.cu.cc/gateshark/game12/ and look at the Title ID > for this game it's 0004000000033B00
2/ Create a txt file named after this TitleID > 0004000000033B00.txt
3/ Copy the cheat title inside the file > [99999999 Points Earned]
Be sure to put the title between brackets ([ and ]) if it's not already the case on the website.
4/ Just below the title copy the code > 08130930 05F5E0FF
Be sure to copy the code as is (multiple lines on the website = multiple lines in the txt file).
If there are several cheats just jump a line and copy the next cheat the same way.
The content of the txt file should look like this:
Code:
[99999999 Points Earned]
08130930 05F5E0FF
[Another Bogus Cheat]
012345678 9ABCDEF0
123456789 ABCDEF01
5/ Save the txt file and put it inside the "cheats" folder on the microSD card
6/ Put your Ridge Racer 3D EUR rom in 3DS format on the microSD card
7/ Follow the instructions to launch the game with selected cheats