Reason 1: Given
We repeat what is given as the first line of any proof. The reason is always "given". Always always always.
Reason 2: Reflexive Property
AC and CA are the same segment: the diagonal shown. The order of the letters doesn't matter. Any segment is congruent to itself by the reflexive property.
Reason 3: HL (hypotenuse leg) Congruence Theorem
The HL theorem says that if we know a pair of hypotenuses are congruent, along with a pair of legs of a right triangle, then we can prove the two right triangles are congruent.