What are the top 5 important concepts/sub-skills a novice should learn?

"... 'Journey to the Chess Kingdom' … is primarily intended for children … The first chapter introduces the reader to the rules ... and teaches ... chess notation. Chapter two is dedicated to basic mating schemes: ... Chapters three and four cover typical middlegame guidelines and plans. Chapter five deals with opening principles, while chapter six provides an overview of the most popular chess openings. …"

https://www.chess.com/blog/Natalia_Pogonina/book-review-quotjourney-to-the-chess-kingdomquot

Watch this video : https://youtu.be/Ao9iOeK_jvU

Also, watch the other videos of this chess fundamental series. 

Another note : Memorize all the checkmating patterns. Good luck !   

1. After the opponent moves ask yourself why he did that: are you in check or does he threaten to capture some of your pieces
2. After you have completed step 1. see if you can capture some of his pieces. Only if neither you nor opponent has any loose pieces nor neither has any checkmate threats should you think about something else to do.
3. When you think you have found your move, before moving ask yourself what could the opponent make next if you make that move. In particular, make sure you are not leaving anything to be captured.
4. In the opening develop all your pieces (do not make the mistake of using just few pieces and leaving the rest of your army home) and castle
5. Learn the basic checkmates (mainly queen+king vs. king and rook+king vs. king) so that you can execute them quickly without a fail (like stalemate)

1. - 3. are about detecting one move threats. Sure you can additionally practice bit more complicated tactics if you want but at your level simple one move threats are missed all the time and the result is mostly decided by who misses these the least so you should first aim to remove these mistakes from your game. Also in steps 1. and 2. make sure to detect all the pieces that can be captured before deciding on a move. For example don't settle for capturing a pawn if you can win your opponents queen instead.

I feel that some of the things mentioned in this thread are bit more advanced that what you should be concentrating. For example doubled pawns or isolated pawns and many other things related to pawn structure. While in principle studying them should do no harm the danger is that you begin to think too complicated: it's no use having a nice pawn structure if you are hanging pieces left and right so detecting simple threats is what you should be mostly concentrating until you can do that almost instictively. Things like isolated pawns are relatively minor detail that only becomes important when you are stronger.

https://www.chess.com/article/view/how-to-start-out-in-chess