SAVE GAMES
Easy : Download a game (offline preferably). Navigate to the game's document/Library folder. Open the files using .txt and find values you'd like to modify ( Ex : money = 999999 ). Profit. P.S, this doesn't work for most games.
Or
Easy : Download a Cheat Engine ((iGameGuardian, GamePlayer, GameGem) I suggest iGG). Search for a value (coins). Change the value of the coins in-game, go back to the Cheat Engine and change it there again. Keep doing it until you find the value you want to change. Change it to 999999999. Profit. P.S, this doesn't work for all games.
Medium : Another way of using Cheat Engines ( Preferably iGG). Basic knowledge as in what is (F32,64 and I32,64). Knowing how to Batch Offsets ( I32 to F64). Knowing how to Rebase memory regions to your preferences.
TWEAKS/PATCHERS
Medium : Use Flex 2/3. Basic knowledge on what variable's are and how they are used (Void, Bool, int, Double, Float and so on). Search for a target class, find the right method that needs to be modified.
Exemple :
Target Class : UserData
Target Method : -(int) coins
Return Value (int) : Pass-through <--- this is what you change to modify the coins value ... P.S, this exemple is very simple. There's several Flex tutorials around the forum that are a bit more detailed which might help.
Or
way : Learn how assembly, ARM language work. Learn how to use a debugger if needed. Now I'm obviously not going to write an IDA tutorial because there's many around the forum or youtube but this is basically the best way to make cheats at the moment ( I think )
Of course, there's other ways to make cheats but this is the most common way to follow when start making cheats. Obviously if you want to go hardcore, learn how to hack using IDA and forget the other options