Ok dude, you REALLY need to use search and read but ok I'll try to explain it like you are 5.
You place your cheat.plg file on your SD card. It goes in the following folder: "sd:\plugin\<TitleID>\cheat.plg", where <TitleID> is the title id of the game the plugin is for.
You then boot your CFW, then run the BootNTR application on your home menu.
When it says "Press HOME to return to the menu", press home.
Then load the game you want to play.
Once loaded you can then activate the cheats by pressing the specific button combination that triggers the cheat you want to activate. These combinations differ from game to game and cheat to cheat, and I cannot tell you what they are since I do not know what game or cheat you are trying to use.
