Understanding Groups | Elements of order 2 | Abstract Algebra

@4:42 I forgot that the first property is "Closure"
Don't get confused.
And one thing I forgot to mention is that the order of an element divides the order of the group.
And the operation defined by me ( a+b*c-d) has to satisfy the 4 properties over the set for the set to become a group. It is just a random operation I took.