Load all the data you want to save into arrays.... Then save all the arrays into a single "Save array" and save as text file in .json format.
If you are making one for simple user settings, that the user will be able to understand and read later, you should study the GetTokenAt get token count.
The second option is the hardest, but if you want users to understand the file it is your best bet.
There is a Save and Load game feature as well, but it will not let you have much control over what gets saved. You can save to the built in save slots, or dump the save into a .json string, and save it as the text file.