Save method and locked level

Hi
I made a game and add some levels. I create a map for my levels so one click on any level and it will open. now my problem is i want to locked levels. the player have to on the first level to open second level. Also i want to make autosave.

Both of those sound like jobs for PlayerPrefs, which let you easily store some data in the preferences file. For example, you could store a 1 for the “Level3_Unlocked” key, and then if you don’t find a 1 for Level3_Unlocked, it hasn’t been unlocked yet. Display a padlock over it or gray it out or whatever you want to do, and ignore clicks on it.

Autosave is a thornier problem; you will have to decide what data you need to store, and how you want to convert that data to/from a string so you can store it in the prefs. There is no quick fix for that, I’m afraid. Depending on how much data you have, it can be a fair amount of work.

The first issue solved.
But still the autosave not clear to me.
There is no tutorials explaining save methods to beginner in game development.
Do you have any site or book talking about this ?

I discuss saving the game in my book but it’s way at the end. Unity in Action: Multiplatform Game Development in C# with Unity 5: Hocking, Joe: 9781617292323: Amazon.com: Books

Thank you.
I will check this book.