What do "32,16,16" (in the Shenzhen tournament) mean?
I have been told that for example in the Shenzhen tournament the qualification board can have 16 female players and only 4 may qualify. It means that each player must win two matches to enter in the competition. But, how do you know that only 4 can qualify? It is not written in the 2018 WTA calendar.
The first part of this question is explained in this question and answer. In the 2018 Shenzhen Open, there were 32 women that competed in the main draw of the singles tournament. Those 32 women were chosen in a number of ways: Some slots in the main draw are reserved for the tournament by their WTA ranking. Some slots are for Wild Cards; the tournament organizers can put anyone they want in those slots. And the remaining slots are for the winners of the qualifying tournament. In this tournament, there were 16 women competing in the qualifying tournament for 4 slots. You can see this in the 2018 Shenzhen Open Qualifying Draw bracket. After two rounds, there are four players left that then qualify for the 2018 Shenzhen Open Main Draw bracket (Those who qualified by winning in the qualifying draw are denoted with a "Q.")
But, how do you know that only 4 can qualify? It is not written in the 2018 WTA calendar.
That information is not available in the "32S/16Q" shorthand notation. It varies with each tournament. For example, the 2018 Sydney International tournament (30S/32Q) had 32 competing in the qualifying tournament, but only for 4 slots, so the competitors had to win three matches in the qualifying tournament in order to get into the main draw. However, in the 2018 Hobart International (32S/24Q), there were 6 slots reserved for qualifiers, so the 24 competitors in the qualifying tournament only needed two wins in order to make it to the main draw.