What is the Nine Mens Morris game, how does it work?

According to the introduction of KL, Nine Mens Morris is a Board game on the Android platform. There is currently a 1.2 version released on Mar 04, 2016, you can see the details below.

Nine Mens Morris is a classic board game.

Each of the two players has nine pieces,
which they put alternately on any free point of the game board.

The game proceeds in three phases:
1.Placing pieces on empty points.
2.Moving pieces to adjacent points.
3.Moving pieces to any empty point when a player has only three pieces left.

If a player gets three pieces in a line - a mill,
he removes one of the opponent's pieces from the game board.

A player has lost, if he has only two pieces left or
if he is not able to make a move with one of his pieces.