Hand and Fist gesture of gratitude
作揖 has 3 variations. One is hold your fists, the other is touch your fists with your palm. The last one is the typical 作揖.
Nowadays, only A and B are still used.
Their usages are roughly same, for greeting, appreciation, say goodbye...
The differences are B is prefered by martial arts people, A is a gesture which anybody could use, C is a traditional gesture used by scholars.