I read that steel/iron/metal/conducting cages, with gaps less than the wavelength of electro magnetic waves, shield whatever is inside from that radiation. But when I put my mobile inside a cooker and called it, it rang. Why isn't this working? Please explain Faraday cage working more in detail.
To be a good Faraday cage, an enclosure needs to be completely sealed, with no gaps larger than about a tenth of the wavelength of the radio waves you want to keep out.
Microwave ovens have a tightly-fitting door, and a metal mesh in the door where the window is. But even they won't completely block a mobile phone signal.
A normal domestic oven may have a glass window, which would let the radio waves in. Even without a window, they have loosely fitting doors with rubber seals, and rubber won't block a radio signal.
See also This Physics Stack Exchange question.