I'll explain what he was meant by using arrays, .
Arrays store data in an orderly fashion, and you can call and insert data wherever you want. Arrays always start from 0, so the first spot for data is 0. To apply this to how you want to save data, you need to make an Array object. This is handy because you can store your level data in the order of levels, making it easy to select data and add it to an overall scoring list, for example. We'll call it array_name for ease of example, . On the Array properties window you'll see a Width, Height and Depth. Width is the total amount of levels you want minus 1 (since it starts at 0, so 13 levels is 12 in the array), and it also represents X, whereas the Height and Depth represent Y and Z respectively. Once made, in an overall Event sheet (one you include on each local Event sheet for each layout) you need to click the following then read on:
System -> Set at X - NOTE: this is found under the Array section
Arrays can hold up to three parts of data in one section, for example 'array = [0,01,02], [1,11,12]'. Each has a X, Y, Z number, but you can use only the X, or the X and Y... totally up to what you need to store, but for what you want you just need X, so you use the above Event code for Set at X. For the X value, put the level number. For the value, put the score variable from that local Event sheet. Let's say the score variable is user_score and represents 16. You should now have the following Event code once you hit the Done button:
array_name -> Set value at 0 to user_score
The above score of user_score (16) is now set to be array_name in terms of positioning. If you want to grab it from the array to have on the screen to check the score, all you have to do is have an element of your choice set the value to array_name.At(0) (0 is the X, if you had three, you'd need 0, 0, 0 or whatever positions you're wanting to grab) and it will retrieve it. That will retrieve the score which is 16 in this example.
Hope this helps!