I already learned the basics in C # (csharp) where should I start making an insim? My goal is to make a cruise insim!

Hey.

If you're just fairly new at this.. There are open source codes you could have a quick look at, just to see how packets and functions are set up. You can find them in the quote

Quote from sinanju :

Use the Search facility, but be prepared to wade through hundreds of posts to try find what you want.
Some old insims to give you a flavour of what you need to know (although they may not use the most current InSim protocol.

LFS Manual - Programming
Example Cruise Server
Open Source Cruise Server
.NET (C#) - [LsGO] Cruise Mod (LifeStyleCruiseGamersOrganization)
Cruise InSim
LFSLapper Cruise

Later on, you can start your own insim from scratch using the InSim.NET Library.
https://www.lfs.net/forum/thread/68564--NET---InSim-NET---InSim-library

Good luck

Oh! Thanks , I'll take a look at everything!