HOw to have gun to make a fps game ?

I want to make a fps game and I don't know hot to put guns ingame and how to put zombies.... Thanks!!

I suggest you work through the tutorials that come with Unity. Unity will do a lot of things for you, but it's not as simple as just clicking a button to add guns and zombies. You'll need to do some scripting and modelling etc.

If I've misunderstood and you already know how to do these things, then...

To create a typical FPS gun, you'd attach the gun mesh as a child of your main camera. To do that, create the GameObject in the usual when, then in the Hierarchy window, drag it onto the camera. Then just position it in the scene editor so that it's in the right position.