SSS (Side-Side-Side) Congruence

SSS congruence postulate (Note the postulate) states that if two triangles $ABC$ and $DEF$ have $$\begin{align*} \overline{AB}&=\overline{DE} \\\overline{BC}&=\overline{EF} \\ \overline{CA} &= \overline{FD} \end{align*}$$ then the two triangles are congruent. That is, if two triangles have congruent corresponding sides, then the two triangles are congruent. The converse is also true--If two triangles have corresponding sides congruent, then the two triangles are congruent.

Because this is a postulate, there is no proof for this and is thus treated as a given in many geometric proofs.

Here is a great triangle drawing tool that can help you out in this topic.