To setup your site logo (as image) or show as text, please go to Theme Options –» Quick Start and choose one of the two options.
Here you have to upload (from Media Library) and insert the image path in order to display your own logo.
If the logo you uploaded looks misplaced or misaligned, to solve the problem you can move logo vertically or horizontally by providing the values in the Logo Offset boxes.
This allows you to enable text-based site title and tagline. You can adjust or choose its font's size, color, etc. for site's title, description. You can also use widely available and popular Google Fonts from there.
Note: the Site Title and Tagline are be coming from Settings –» General