How do I setup the Login Page to work with requireLogin? I want to create a login page.  It would be a Single. 

The URI is set to login.  So how do I name and map the twig file?  

I tried: 


creating a login folder under templates.  
naming the twig file either login.twig or index.twig
setting the template location to login/login.twig or login/index


Neither approach worked. 

How do I setup a login page so that when I use requireLogin the login page is in the right location for loginPath.  At the bare minimum, where is the easiest location to place the login path?
You didn't specify Craft 2 or 3, but I'm pretty sure this answer applies to both.

The template should live at templates/login/index.twig or templates/login.twig. Craft will resolve to both of them.

I tested this on a fresh Craft Pro install and created a Single with a template path of login.  There is a templates/login.twig with the login example here: https://docs.craftcms.com/v3/dev/examples/login-form.html and a templates/test.twig that only has {% requireLogin %} in it.

I logged out of Craft, then went to mysite.com/test in a browser and was successfully redirected to mysite.com/login that rendered the example login template.