In a non-SXA website where you are using Sitecore MVC, you are working on the...

To implement a layout in Sitecore MVC, you need two things: a layout.cshtml file and a layout definition item. The layout.cshtml file is the Razor view that contains the HTML markup and the placeholders for the renderings. The layout definition item is the Sitecore item that references the layout.cshtml file and provides metadata for the layout, such as the name, path, and device. You can create both of these from Sitecore Rocks or from the Content Editor. References:

MVC and renderings

Add a form to a webpage