White is in shortage of liberties. Look how helps.
If here, then White plays at , threatening to connect at a. If Black plays b to prevent this, then White can prevent a second eye to the right of b, and kill, with c or d
Note that must not be played here! Then and lives, after sacrificing the two Black stones on the right. Of course, if makes the mistake of playing at to save the two stones, White plays the placement at and Black loses everything instead.
White can answer at or at a. After , white a and black b do not create a ko, as shown by the next diagram.
and try to make a bent four.