How do you make vegetable seeds?

Question

I mean from existing vege plants when they go "to Seed".

Answer 1

You don't make vegetable seeds. They grow.

Answer 2

Different vegetables make seeds in different ways and how you harvest them depends on the plant.  Some, like tomatoes and peppers have the seeds inside the fruit.  Others, like peas and beans grow the seeds in a pod, while still others such as radishes, carrots and spinach grow the seeds from a little flower on top of the plant.  

Answer 3

buy the seeds from an gardening store