Minecraft calls them commands rather than cheats, and they are typed into the chat window. They are off by default in survival worlds, which is the first thing to sort out.
Turning them on
When creating a world, switch Allow Cheats to on. For a world that already exists, open it to LAN from the pause menu and enable cheats there — that works for the current session without changing the world permanently.
Press T to open chat, or / to open it with the slash already typed.
The ones worth knowing
/gamemode creative — switches to Creative: flight, no damage, unlimited blocks. /gamemode survival switches back.
/time set day — skips to morning. There is no waiting and no bed required.
/weather clear — stops rain or a thunderstorm.
/give @p diamond 64 — gives 64 diamonds to the nearest player.
/gamerule keepInventory true — you keep your items when you die. Arguably the single most quality-of-life change in the game.
/effect give @p night_vision 999999 — night vision for a very long time. Caving without torches everywhere.
What @p actually means
Those symbols are target selectors, and there are only four worth knowing:
@p— the nearest player (usually you)@a— all players@s— whoever ran the command@e— every entity, including mobs
Once those make sense, most commands you find online stop looking cryptic.
The trade-off
Enabling cheats in a world disables achievements for it, and that flag stays with the world permanently — turning cheats back off does not restore them. If you are working towards achievements, use a separate world.
