Mate with a knight and bishop?

 So one of my friends send me this in the messages and I am so confused so please someone tell me how this mate occurred and how to do it.

thanks a lot, I learned from the video.

1. My friend send me this, this is his opponent
2. Can you not see that the bishop is guarding the f8 square

Additionally you can practice here: https://www.chess.com/endgames/checkmates/bishop-and-knight-mate/challenge

i did it 5 times on endgame trainer in under a minute.  😁

good for you.

Checkmate with a bishop and knight, although difficult, can be forced. In your example Black made it easy by staying in a corner where checkmate can be forced (you can only checkmate in a corner the same colour as your bishop). The best defense involves moving the king to the 'wrong' corner (so in your example, Black should have moved to a8, a square where it cannot be checkmated).

There are two well known methods that can be used when performing a bishop and knight checkmate, these being the W method and Deletang's triangle method (note: you only need to know one of these; choose which ever one you find easiest/can win every time with). Both of these methods involve getting the king from the 'wrong' corner to the 'right' corner, which is essential to know with this checkmate.

I said my friend send me this .

not my fault that black sat there.

ok?

but the game already happened......

that is amazing!

1. force king in to the side of the board

2. you must mate in the same color corner as your bishop

3. often the winning mechanism involves forcing the king from the wrong corner color to the right, with a W maneuver by the knight.

4. the hardest point personally, is the attempt of the opposing to wiggle out of being forced into the corner and attempts to flee to the other wrong corner, at this moment, there is a specific bishop and knight combination which forms like a block of illegal squares which forces the king back in the box

5. once he is in the right corner, you just have their king back and forward and its just a matter of luxuriously moving the knight to the right configuration to deliver the mate.

All of this easier said than done!

They are also other methods, there is one where where you form smaller and smaller triangles, but i personally prefer the W maneuver 

you gotta try it multiple times with a human. Engines will always go for the longest mate sequence which is not always the most challenging. 

In the forum topic example - it was somewhat incidental because the side with the pieces has winning pawns anyway - in addition to his two minor pieces.
Will anybody investing time in the book win of N+B versus lone King - ever actually encounter that in any game in his/her entire lifetime?
I would say its unlikely.
Queen versus rook is more likely.  But its still rare.

Regarding N+B versus Lone King - as an 'intellectual or chess Exercise' - 
hey why not?

So far - Deletang's triangles haven't been mentioned yet in this forum.
Unless I missed it.
But that's a 'solving method'.  And a better one I'd say.
Understanding that Lone King can be confined to a Shrinking triangular zone of the board - defined by the bishop.
Ideally - the attacking King plugs one end of the slanted line (hypoteneuse) of the right-angled triangle.
The knight and bishop form a wall at the other end - making it impossible or futile for lone King to approach either piece.
Then Zugzwang is used to shrink the Triangle.
Becomes a fatal 'Bermuda Triangle' for LoneKing.
Ideally - the 90 degree Apex of the triangle - is defined by the corner square that is the same in color as the bishop.

The task becomes much more difficult if there are misinterpretations of 'keeping lone King on the Edge'.
With best play - lone King will try to be confined to one of the two 'wrong corners' of the board.  He can't be mated there.
Then players struggle terribly to learn/memorize how to keep him on the edge and force him to one of the two correct corners.
Ironically - its they who are 'on edge' while lone King threatens to 'escape out into the Interior' 

i learned what to do & got out of there.

I've been proficient in it.  But I've never remembered thoroughly.
The whole exercise would be better - if a way can be devised to Efficiently connect up the semantics with concepts that cover all possible such positions.
But that way perhaps doesn't exist.
Its too tricky to have a 'formula'.  
Whereas many endgame positions do.  They have a 'formula'.
But that won't work either for ambitious players - without insights into tactics.  

There are many internet pages on Deletang triangles.
Here's one of them:

https://en.wikipedia.org/wiki/Bishop_and_knight_checkmate#Del%C3%A9tang's_triangle_method

Deletang's triangles.
People can google it so they have the foggiest idea about how to mate with knight and bishop against lone King.
I avoid google myself.  I prefer DuckDuckGo.  Its a better search engine for multiple reasons.