How to add the server in Traffic Lights? Please Help.

The use is clearly stated in the law
https://www.lfs.net/forum/thread/89159-LFSLapper-adding-ISP-OCO-packet-%28StartLight-Control%29

You cannot add AutoX objects ( StartLights etc) as a demo user.

How do I add this code ?

There is a file in post 9. With an example how to use the code.
https://www.lfs.net/forum/post/1904406#post1904406

To use that code, you must use the AutoX startlights. Which you cant because you are a Demoracer.

If you want to add/use those lights you must buy a s1/s2/s3 license.