it depends on the triangles that you have,you will use one of them (SAS,ASA,SSA) for example
-if you have that the triangles has two equal sides and their angle equal too you use SAS to conclude that the triangles are congruent.
-if you have that the triangles has two angles and the side between them equal, you conclude by ASA that the triangles are congruent.
-Finally, if you have that the triangles has two equal sides and a angle equal too, you conclude by SSA that they are congruent.