I just checked out lots of works (and scripts) from others, but I have no idea how they worked?

Can someone do me a tutorial out of this?

I'd guess you mean infinite side-scrolling terrain, where the terrain moves left or right infinitely.

I am not going to explain the side-scrolling engine in detail, but I will explain how the infinite terrain is achieved:

Most scrolling engines use lists, where each list item may correspond to a vertical chunk of the generated world. Multiple items rendered together fill up the whole screen. When you reach the end of the already generated data, a randomiser will create a string of characters for the next area, and put it in the next list slot.

Edit:
I just made this simple program infinite so you can understand: https://scratch.mit.edu/projects/113005502/
It is just 3 scripts, but could be condensed into 2.

Here https://www.youtube.com/watch?v=bAJxFQ9x8zE

Hey Guys! What do you think about this terrain generator?
https://scratch.mit.edu/projects/420299235/

I have a awesome example. Just backpack the map and enviroment sprites!
HERE

Please don't necropost on old topics! You have just bumped someone needing help now off of the front page, making it much less likely for them to get help.

Thanks to everyone who offered their help, but this thread is pretty old at this point so I don't think the OP is looking for an answer anymore. Please check the date and make sure the thread is still relevant before posting. Thanks!