3D shape attributes

I am the poorest shape in the world. I have no straight sides, no vertices and no flat faces. Who am I?

I have no vertices but I have two circular faces. Who am I?

I have one flat face and one vertex. I can be a water tank, a pipe or a candle. What am I?

I have 5 faces, and my base is a square. I can be a pyramid, a tent, or a mountain. What am I?

I have 6 faces. 8 vertices and 12 edges that are the same length. Who am I?