Studying beyond the opening? I was watching the following video on the Ruy Lopez (Spanish Game) - Variations with 3...a6. The video is almost 1.5 hours and it pretty much goes through all variations with 3...a6.
As I was going through the video, I got lost and frustrated because it seemed to much to take in and I was trying to plug in all the possibilities into Chess Position Trainer.  So this got me thinking, is it necessary to learn all these variations that go beyond the opening and by beyond the opening I mean once you get past Bb5 in this particular case?

For example, in the video, they went over the deferred Steinitz defense:
1 e4 e5 2 Nf3 Nc6 3 Bb5 a6 4 Ba4 Nf6 5 O-O d6 which was enough for me, but then they continued with white's most popular replies on move 6 and continued with black and I didn't know where to stop.
is it necessary to learn all these variations that go beyond the
  opening?


I would say no it is not necessary to focus on the opening that much until you are playing chess at a very high level. If you are a beginner the best advice would be to dedicate most of your study time to middlegame tactics and strategy, as well as some basic endgames. Here is a quote of Capablanca on the matter 


  I have very often met players who know the openings by heart; that is
  to say, they have learned from some book or other and they think they
  know them very well. And indeed they do know them very well by heart,
  but nothing more. They do not understand the objectives behind the
  openings and therefore do not know what advantage has to be taken of
  them, and it often thus happens that they lose. And they lose because
  they have studied the openings badly without learning them or because
  they have not studied them in depth. It is clear that this can happen
  to anyone, but it is more likely to happen to someone who studies only
  the openings than to someone who dedicates himself to study of the two
  other phases.


The quote is from a lecture you can read online

ps. You will probably also benefit by studying the games of the masters... for example, by using a book as Irving Chernev's Logical Chess... Good luck!