Theory:

The four whorls:
Calyx and corolla are the two outermost whorls of a flower. As they do not directly take part in reproduction, they are also known as non-essential or accessory whorls.
As androecium (stamen) and gynoecium (carpel) take part directly in reproduction, they are known as essential whorls.
 
stamens and pistils.jpg
Androecium and gynoecium
Androecium:
It is the male part of the flower that is composed of stamens. Each stamen is made up of a filament and a small pouch-like structure at the tip called the anther.
 
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Structure of stamen

The pollen grains are formed in the pollen sac's anther.
Pollen grain:
 
Figure_32_01_06f (1).jpg
Structure of a pollen grain
 
Pollen grains are typically spherical in shape. They have a two layered wall.  Exine is the hard outermost layer. It has germpores, which are large openings. Intine refers to the thin inner layer. It's a cellulose and pectin-based thin and continuous layer. The vegetative and reproductive cells are the two cells  found in mature pollen grains.  The nucleus of a vegetative cell is a large one. The generative cell splits into two male gametes during mitosis.
Gynoecium:
The female part of the flower which is made up of carpels is known as gynoecium.
1024px-Gynoecium_diagram_for_Simple_wikipedia.jpg
Gynoecium
  
It consists of three parts:
  1. Ovary
  2. Style
  3. Stigma
The ovary is a structure in which ovules are present.
 
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Structure of gynoecium
Reference:
https://www.flickr.com/photos/rayinmanila/20561557586
https://upload.wikimedia.org/wikipedia/commons/a/a2/Figure_32_01_06f.jpg
https://upload.wikimedia.org/wikipedia/commons/thumb/b/b8/Gynoecium_diagram_for_Simple_wikipedia.jpg/1024px-Gynoecium_diagram_for_Simple_wikipedia.jpg
https://upload.wikimedia.org/wikipedia/commons/1/1d/Figure_32_01_05.jpg
https://upload.wikimedia.org/wikipedia/commons/thumb/6/6e/ABC_Model.svg/512px-ABC_Model.svg.png