Composer will install it in whatever directory you're running the command in, unless you specify a full path... copy and paste it? Or, create a VirtualHost in Apache.

Windows user here too. As mentioned composer will download into the current folder you are at with the command prompt. Composer doesn't care what web server you are using, and it shouldn't. Here is what I do on XAMPP when creating a new L4 app. Open a command prompt.

cd c:\xampp\htdocs
composer --create-project laravel/laravel new-app-name
cd new-app-name
composer install

The first command navigates to my default web server folder. The second will create the subfolder c:\xampp\htdocs\new-app-name with the laravel framework structure. The third command changes to the new subfolder. The fourth command will download the remaining 3rd party framework packages.

Then if you open a browser to http://localhost/new-app-name/public/index.php you should see the default L4 screen. I will then usually create an alias or virtual host for that folder, so I don't have to have the /public/ folder in the url.