Idon't know where there are two similar triangles . i'm so confused !

Two similar triangles would be Triangle XBY and triangle ABC. You have to look at the small and large aspects of a diagram.

The first triangle is the entire figure except for the line running across the middle (triangle ABC). The second triangle is created with the line running across the middle because it forms a mini one at the top half of triangle ABC.  

Your two triangles are triangle ABC and triangle XBY. 

Hope this helps!! :)

Idon’t understand sorry