How the site logo should be made and where it should be placed. Let's start with the main thing, from my own observations I realized that the file must be logo.png and is located in the root of the site. Its size should not exceed 500 pixels in width and height. Moreover, important images other than the logo may be in the root folder, although there are no recommendations for this from Google. The alt tag should also be included for better search results.

It is advisable to create a site icon  from your logo or an approximate one for visual presentation . In this case, the visitor will have a better perception and understanding. A logo, like a favicon, cannot have a large palette of colors, a few and no more, but it is better that you have it in vector form initially. 

Background transparency for logo.png file? A common question is, here you need to see the images themselves, sometimes, as they say, there should be a backing. 

Can there be multiple logo files? I think so, you can just call them logo2.png and so on. For example, on the main page there is a logo for the header, it is one size, the logo in the text is another and in the footer there is a third. 

And lastly,  the path to the logo.png file should be indicated in the micro markup on the main page. Although in other pages and news publications you can set your image to be pulled up. And this is very correct!