How to add custom images to header I would like to add some custom images into the header block of my website and the problem is that I don't know if I should modify some php file or if it is possible via admin panel. Which method is better and if it is better to modify a file, which file is it and where is it located.

Thank you in advance.
The simplest way: Add a block at admin/structure/block/add. Add the html for your images directly into Block body. Make sure the text format is Full HTML. Assign your block to Header region.

Before this, you need to upload the images on your server. You can either upload them directly to your theme folder or create an image content type with image field and use that to upload your images.