SSS stand for Side Side Side, so the truangle must identify all it's sides. To identify sides it uses lines through the side like in B where 1 side has 1 line, 1 side has 2 lines, and the other side has 3 lines. That is the side identifiers, and because each side in B matches with 1 side in A, means that A and B are congruent because they have the same sides, so SSS.
This is confusing to explain, if you have any questions post them in the comments.
