When we look at congruence, we are usually dealing with proving that two triangles are exactly the same. To establish this, we need to know two things about triangles:
1) Triangles have 3 sides
2) The angle sum of a triangle is 180o
There are only 4 ways to prove that two triangles are congruent. They are literally the only things that you need to remember.
RHS: Right Angle, Hypotenuse, Side
We use RHS when we have two triangles that have a right angle, an equal hypotenuse and one other equal side.
SSS: Side, Side, Side
We use SSS when we have two triangles where each of their corresponding sides is the same length on both triangles.
SAS: Side, Angle, Side
We use SAS when we have two matching sides between the triangles and the angle between those matching sides is the same on both triangles.
AAS: Angle, Angle, Side
We use AAS when two angles and one side of each triangle match each other.