Hey Sandra!
I’ll go over the questions one by one:
1). To display the custom header on a page, make sure you’ve chosen the needed header type from the drop-down list in the “Custom Header” box below the text editor area, while in the page edit mode.
2). To decrease the empty space above the header, please go to “Appearance – Editor” and add the following line to the “style.css” file (should be opened by default):
#header-top { margin-top: 20px !important; }
and hit “Update File”. You can of course replace the “20” value with any other figure you like ;)
3). To use a logo, just upload it through the theme options panel, “Page Elements” tab. Let me know if I understood the question correctly!
Best,
Andrew | Satori