How to make an simple Save&Load system for horror game ?

Hi everyone, this is my first time on this web's ask community;

I'm a beginner and i want to do an simple system script that can Save&Load a scene number.

I have an horror game that have 3 levels - 1 is "Forest" - 2 is "Valley" - 3 is "Dungeon"

In each level, the player must retrieve a number of key order to take a portal that leads to the next level

I would, for example, if the player reaches level 2, then the next time he comes to the game, a "Continue" button on the main menu leads directly to the beginning of the level 2. Same as if it reaches level 3, the game will lead to the beginning of level 3.

However, if he is killed, the level data are erased and the player starts at the very beginning (level 1).

I hope I have explained clearly enough, I do not speak English very well. If you need more information, do not hesitate.

Thanks you ! :)