The first is "belonging", which means that an element belongs to a set, that is to say, there is this element in this set.

The second one is generally a "set", and all braces are "elements" in this set.

The third {|} also represents a set, but with constraints:

The area in front of the vertical bar is generally used to indicate the "element" of this set, and the area behind the vertical bar describes the characteristics of this "element". take for example

{y | y>0 and y∈Z} mean that all unknown elements in this set are represented by Y. If you want to belong to this set, you have to meet some conditions. What are the conditions of these unknown elements >; 0 is also an integer, so the y in front represents these unknown elements, followed by the conditions that describe these elements, that is, the constraints on the existence of the set.