Question

when do we say two triangles are similar​

Answer 1

when two triangles have similar base similar height in simple words when they are congruent

Answer 2

If two pairs of corresponding angles in a pair of triangles are congruent, then the triangles are similar. We know this because if two angle pairs are the same, then the third pair must also be equal. When the three angle pairs are all equal, the three pairs of sides must also be in proportion.