How to create custom.css you can watch in this tutorial (it’s for Legenda theme but the process is the same).
2. You can add your code in Appearance > Widgets > Place in header top bar or edit the current links in the file wp-content/themes/royal/framework/shortcodes.php (lines 1729-1761) and change the links to yours, for example for twitter, replace the link https://twitter.com/share?url='.$permalink.'&text='.$post_title.' to your Twitter account link.
3. You can edit it in wp-admin > Settings > General.
Thank u for the answers Eva, very usefull, 2 questions more if is possible:
3. Where i can remove or edit the content of the left div beside the Logo in the image?
You said me i can edit it in wp-admin > settings > general, i know it but i dont want change the text, i will like change this div for a custom HTML i create with image or other objetcs, i can not change my General setting because i use it for SEO on Page.
If i delete my general message the div shows empty but show border and icon, i want remove it from left logo and change for a custom div i make with images or something.
2. Is possible that a row in visual composer not show in mobile devices? I dont want show this div in mobile devices.