How is this the best move?

I'm trying to pick up pinning so I started some puzzles about it.  I came across this.

Why can't Black's King just take the White Rook?  How is it Checkmate (or Check, I forget what # means)?  If the King can take the Rook, how is this a smart move for White?

The rook is protected by the b2 bishop

A famous example of the dangerous weapon of bishops on the other side of the board. If there's any thing almost all casual players will miss, it's this.

Yes, this is checkmate.  That means that white wins since black's king cannot escape check on the very next move!  Black's king cannot capture white's rook since white's bishop on b2 is protecting the rook.  

This checkmate pattern is pretty common!   

It is called the OPERA MATE

there's the bishop on b2

as a beginner, please note that the bishop is pulling double duty: first it protects the rook, as oft mentioned already, and SECOND, it prevents the king moving up one square to get out of check, the bishop covers the square.  

Bishop far away. Many times, I admit, I've been checkmated with a queen and bishop for this because I haven't paid any attention...

I can only see half the board.

Never mind. I have to turn my phone sideways duh.

Here for your amusement and education I found this in my database - The original 1858 'Opera House' game with annotations by R J Fischer! /enjoy