Instead of telling the OP to "RTFM" why not try to actually help him out instead? Does Google work; sort off, there is
a lot of bad advice out there. Also: you cannot assume that your Google search results will be the same as the OP. So just sending him off to Google is IMO just bad & lazy advice.
So.. how to start with a server....
It's easier than it may seem. Start your launcher, open the menu (click on the three lines in the upper right corner) and then check the "Launch options" tab. You should have an entry called "Latest release", click on it and you'll find a link called "Download server" in the upper right corner. Click on that too and now you'll get the actual server jarfile.
Next step: be sure that you installed Java in a proper way. Then move the jarfile you downloaded in a separate (new) directory and double click on it. It should now open up a window and start up. For a quick moment anyway, because it will also automatically stop again.
You'll notice that it has created some files. Edit "eula.txt" and change false to true. Then re-start the server.
Eventually you'll end up with something like this (other than the browser window and such of course ;)):

Congratulations, you're running your own server at this point. Be sure to check the contents of that directory because you'll have a lot more files now. Especially "server.properties" can be a good study because that allows you to re-configure your server.
For more information I'd like to point you to the tutorial on the Minecraft wiki
here, and
this page can help you to learn more about that server.properties file.
Hope this helps you out a bit!