nav top bar menu for twenty fifteen theme

Hi,

Attachment is my site home page screenshot. In this screenshot, I have two questions would you please help:
1. How can I create a navigation menu bar located on the top of the homepage screen and the left/right side should be located as the arrow indicated in the screenshot?

2. In the screenshot, as you see on the right there are a lot of "X", how can I make my screen home page completely full page so I can get rid of the extra spaces indicated by 'X"?

Thank you for your support,