[Clavius]

Hello there!

I see you are new here.
I suggest you start with the basics, which you can find here: https://sampwiki.blast.hk/wiki/Scripting_Basics
You should also check out the pages listed here: https://sampwiki.blast.hk/wiki/Script_Examples

Also have a look at the general PAWN-related documentations, too! You can download them from this link:
http://compuphase.com/pawn/pawn.htm#DOWNLOAD_DOCS

But, to answer your question, here is a tutorial about automatic gates: https://sampwiki.blast.hk/wiki/Automatic_Gates
and here is an example script of gates: http://forum.sa-mp.com/index.php?topic=96947.0
And you can find more tutorials on this page: https://sampwiki.blast.hk/wiki/Tutorial
You can always find reasources on the Wiki, use it, read through the functions and callbacks.

Good luck with learning scripting!