When I create the partial design for example footer or header how to get the "rendering layout file"? Is it automatically created and I just edit it and if it is not, how can I create one?
For example, does it exist in Layout -> Renderings -> ... (name of the partial design).
A Partial Design in SXA is not the same thing as a Rendering. There are no controllers, views, rendering items etc...
A Partial Design is effectively a Sitecore item with presentation applied to either the Shared or Final layouts.
Partial Designs are then added to a page via the pages associated Page Design.
At render time, Sitecore will gather the pages layout and all the partial designs layouts and merge those together into a fully composed page layout for rendering.
As Sumit mentioned in his answer, to add components to a Partial Design, you simply edit the design in the Experience Editor, much in the same way you do on a Page.
Some things to note. A partial design will have the same placeholders as a page, OOTB, SXA will give you header, body, and footer placeholders. If you use the header placeholder on your header partial design, this placeholder is no longer available to pages that include that partial design. So if you want to allow components to be placed in the header area on your site, you will need to include a Container component on your partial design, this gives a placeholder that can be used on pages. AFAIK, this is done to simplify the merging of the final layouts when composing the page.
In SXA when you create a partial design for the footer, header, or any, it will not give you a rendering layout file, where you can update the HTML. It's an OOTB feature.
You can create a partial design by going into your SXA site -> Presentation -> Partial Design. And using the insert option, you will be able to create a new one.
After creating the partial design, you can add renderings to this by using Experience Editor or going into the item presentation details.
