How do I add a combinator to my style?
You can only add combinators to child selectors. Add a child selector and combinator will appear in the Style tree.
Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
No, you cannot layout forms with Acquia Cohesion.
You can style tables or forms through the use of base or custom styles.
You don’t have to add units unless you want to use a specific unit or you’re adding Custom CSS properties.
You don't. You apply a Descendant selector. These use a (Space).
The Youtube video embed is responsive so it should expand to the width of its parent. If you do need to set a width you can apply the Width CSS property through the Style Builder.