You must find the corresponding parts of the two triangles first. Then, you must find the angle measure of one pair of corresponding angles. You would then find the length of a pair of corresponding legs or sides in between the two angles. Lastly, you would need to find the angle measure of another pair of corresponding angles.
If you have a corresponding pair of congruent angles, a pair of congruent, corresponding sides, and another pair of congruent, corresponding angles, then both triangles are congruent.
Here’s an example:
Notice that the triangle’s side is in between the two angles; this is required when using ASA.