A lot of released games having micro transactions and annoying restrictions. When this games making an inside explosion of stress in your body, you can start thinking about change it or just disable it. This short history is describing why game cheating profession was committed.
Game cheating is of course methods to change something implemented in software by game developers to adapt it for cheater request. In a lot of cheating concepts.

Firstly, you can edit game not-encrypted files. For example, configs or quest scripts. It is very easy method, because sometimes only notepad.exe in only required to make something amazing. But what you can to do? When it is single-player game, your creativity is only restricted for encrypted and compiled game code. From this game cheating tactic evolved home-brew communities which editing games, making add-ons and mods. Of course, when you are share edited game files, you probably break the law.

Second game cheating method is using injection code to application memory. Do you know about cheaters in first person shooters like Counter Strike: global offensive? This hacks based on injection code to: firstly, disable inbound game anti-cheating software. Secondly it adding to game execution code lies with aim bots or editing 3d engine parameters to show another player (wall hack).
Very easy concept to make an injection to game memory is free application Cheat Engine. It is allowing to edit game variables. For example, you can add to inventory new items. Any objects in game must be stored in memory in putted together data arrays (in mathematics it is very simple like data matrixes). By Cheat Engine you can add new objects or replace id from old item to new.

Moreover, game injecting allowing cheater to speed up or speed down game clocks. Like in Metin2 MMO game – speed hacks.

Thirdly and finally tactic to cheat games is (only for online productions) edit in ‘air’ packets. Applications for this Is Wireshark. To inform you how this concept works you need to know about TCP/IP and/or ISO/OSI. In one word, it is like in above option but in communication with server. You can inject code to server or client or both by Wireshark.