Unity problem with a plane

Hey guys, can you help me with this? I want to create a game very similar to a game named "Teeter Pro" on google play shop. I'm a beginner in Unity and i want to put in a plane a hole, where a ball will be fall- when ball fall in, it will be a restart game or win ( you know ). How can i put a hole on the plane, there is a question. Just in Unity or i have to create it in another program and then import it to the Unity? I made it in a Blender, but when i imported this model to Unity it doesn't work- i dont know how to explain. Emm... in a plane won't be a hole, just this "cylinder" went through a plane ( you know what i mean xD, ). Please guys, help me with this problem.

There is a SS on what stage i'm

http://zapodaj.net/9b379a72a77f5.png.html

Sorry for my bad English, i think.

 

Normally you would use an external program if you want 3d models in your game, the built in unity shapes are mostly there for prototypes. Download Blender (free) and watch a few videos to learn how to add vertices, edges, and extrude. Then make your model and import it into unity.

 

I made my model what i said, but it doesn't work. I made a hole, then i imported it to unity, add on plan and what?. A plane was i a hole. My model through into a plane. EHhh, better i upload SS's

Its looks like this right now:
http://zapodaj.net/c650c14e8b024.png.html

But i want to looks like THIS!:
http://zapodaj.net/9448a814a73e1.png.html

 

Meh, now it looks that. That model through into a plane... I dont know how to delete a floor in this place where is a model.

http://zapodaj.net/c0d2d4ab3f5a2.png.html