How can you show that a triangle has three congruent sides?

There are 4 rules for congruent triangles:

SSS-->This means side,side,side and to prove triangles are congruent with this rule, all the sides will be the same on both triangles.
SAS-->This means side,angle,side and to prove triangles are congruent, you must have 2 sides and an angle the same on both triangles, but the angle MUST be in between the 2 sides.
ASA-->This means angle, side, angle and to prove triangles are congruent with this rule, you must have two angles and a side the same, but the side MUST be in between the two angles.
RHS-->This means right angle, hypotenuse, side and to prove triangles are congruent with this rule, you must have a right angle in both triangles, and have an equal hypotenuse and side.

Hope this helps:)