object not colliding with another object,,.but getting merged and passing each other.

I have a plane and a character(made of a sphere and capsules) but the character is not colliding with the plane rather it gets merged with the plane and again passes off it to the other side I am new to unity3d…need some help here…

Check if either ur plane game objects. Is trigger option is enabled on the inspector if yes uncheck is trigger
If u are using first person controller they have attached colliders so that is not a problem if nothing works simply

Add a box collider to ur plane object and resize the collider according to ur plane’s size

Or create a box and resize it until it looks like ur plane.

Take a look at this tutorial and the rest in the physics series, it will explain what you are looking for.