How do I make a virtual world in Unity?

Just like there's no formula for creating the next big hit MMO / replicating Gears of War or creating your own version of Ratchet and Clank, you won't find a "Creating virtual world software solutions: A-Z" manual anywhere. If it was that simple, the industry would be quite a bit smaller.

I'd suggest you start out and get to know Unity better by going through the officially given tutorials and then expand your knowledge with networking tutorials and community created tutorials.

All of this assumes that you have some understanding of programming, 3D math and networking. If you lack this as well, jump onto amazon and see if you can find some well recommended books on the subjects.

The task you're considering is not exactly a simple one, but best of luck.

If you are new to game development, I would recommend doing this:

Create a REAL simple 2d game, one where you control a colored sphere and your friend(s) control other colors.

Get them to shoot at each other, then handle something like scoring, etc.

Once you have that working, and are somewhat understanding the basics of networked gaming, look at how to create your own 3d environment. A SIMPLE one. Heck, reuse the island demo. Or just create a flat plane with some grass, and a couple of trees.

Now, duplicate the colored spheres shooting at each other, but now with your 3d environment.

By that time, I think you'll start to see the challenges of your request. Add some npc characeters that have a simple AI, then make them move around, shoot at you, etc. This makes it even more challenging.

Then add some simple quests/goals.

Something that I struggle with is, I have big dreams and ideas, but if I just dive in and try to create the next awesome space game...I FAIL, because making cool, big games is a huge undertaking that normally takes people with a lot more experience and natural talent than I have YEARS, and LOTS of money.

So

Start small. When you are trying to understand a new concept, like network programming, ai, pathing, etc...just create a simple project focused ONLY on that! Don't try to understand pathfinding, AI, networking, and such all at once. Understand each part, and get a little sample where it works.

Don't expect to learn how to create awesome fully eye-popping 3d models, while you are learning how to do your game (unless you are already able to create them). Just use a sphere for your models, or something. If you get the game mechanics working...worry about having nice looking models later.

Get ready for frustration, and a long haul. Unity is an awesome tool...but doing what you are asking takes a long time. The forums and answers are nice...but not really a repository for knowledge. There is some information there..but you will spend many hours scouring the internet and even watching youtube videos. I'm currently frustrated because I'm TOO DUMB to grasp effective uv unwrapping/texturing on my models :( :(

The key is...start building your knowledge on various aspects of game programming (like by making simple games that uses these parts), then you will have confidence when it comes to bigger projects.

Just my $0.02.