To highlight the section of the next slides in a ToC you need to start the section officially using
\section and then use
\tableofcontents[currentsection] in a frame:
There is also other options to
hideallsubsections as well, all of them simply change the
They are all explain in the
beamer manual, page 100pp. Here the important part:
sectionstyle=⟨style for current section⟩/⟨style for other sections⟩ specifies how sections should be displayed. Allowed
hide. The first will show the section title normally,
the second will show it in a semi-transparent way, and the third will completely suppress it. You can also omit the second style, in which case the first is used for all sections (this is not really useful).
subsectionstyle=⟨style for current subsection⟩/⟨style for other subsections in current section⟩/
⟨style for subsections in other sections⟩ specifies how subsections should be displayed. The same styles
as for the sectionstyle option may be given. You can omit the last style, in which case the second
also applies to the last, and you can omit the last two, in which case the first applies to all.