How to remove the square on the back of title, and can i add logo on the top left?

If you want to remove the square section in the theme, you can log in to Dashboard > customize > cover image then remove the color in the “Site Title Background” section:
See the screenshot: http://prntscr.com/5alz95
Also, currently, out theme does not support to add the logo in the Top left site.
Hope this helps !