congruence occurs if 3 sides in one triangle are congruent to 3 sides in another triangle.

Yes, you are correct. This is known as the Side-Side-Side (SSS) postulate in geometry. If three sides of one triangle are congruent to three sides of another triangle, then the two triangles are congruent. This means that they have the same size and shape, but may be flipped or rotated. Here are the steps to prove it:

1. Identify the given triangles you want to prove congruent.
2. Check if the three sides of the first triangle are congruent to the three sides of the second triangle. You can do this by measuring the sides or by using given information.
3. If all three sides in one triangle are congruent to the corresponding three sides in the other triangle, then by the SSS postulate, the two triangles are congruent.
4. Write a statement to conclude that the two triangles are congruent by the SSS postulate.