I read online that wormholes are formed when the fabric of space time is bent, but visualisation was the bending of two dimensional space with a three dimensional object. So what bends three dimensional space to create three dimensional wormholes?
Gravity is often visualised as a 3D object bending a 2D-surface. I think this comes from the fact that we are not particularly good at visualising a 4D objects that bends a 3D-space.
Maybe another way of thinking is in terms of density. Instead of a 2D-surface think of a room filled with a material, which density varies with position. In the center is something heavy. There, density is much higher than at the edges of the room. So, mass attracts space-time-density, so to say -- or where the space time density is higher, there is something massive.
Hope that helps.